This is an overview of Isaiah 42-48, and key verses that may shed some light on what is being said in Isaiah 45:7, which states:

"I form the light, and create darkness: I make peace, and create evil: I the Lord do all these things."

My understanding from what I read this in Isaiah chapters 42-48 is that God was saying He is the only God.  He won't give any glory to the idols that were being worshipped.  Israel was trusting in carved idols and metal images.

Here are some verses for reference:

1.  Isaiah 42:8

     I am the Lord; that is my name; my glory I give to no other,   

nor my praise to carved idols.

2. Isaiah 42:17 

They are turned back and utterly put to shame,
    who trust in carved idols,
who say to metal images,
    “You are our gods.”

3. Isaiah 42:25

So he [God} poured on him [Jacob/Isreal] the heat of his anger
    and the might of battle;
it set him on fire all around, but he did not understand;
    it burned him up, but he did not take it to heart.

4.  Isaiah 44:6b 

I am the first and the last, bedsides me, there is no god.

5. Isaiah 44:12

The ironsmith takes a cutting tool and works it over the coals. He fashions it with hammers and works it with his strong arm...

6. Isaiah 44:13

The carpenter stretches a line; he marks it out with a pencil.[a] He shapes it with planes and marks it with a compass. He shapes it into the figure of a man, with the beauty of a man, to dwell in a house.

7. Isaiah 44:17

And the rest of it he makes into a god, his idol, and falls down to it and worships it. He prays to it and says, “Deliver me, for you are my god!”

8.  Isaiah 44:24-25

Thus says the Lord, your Redeemer,
    who formed you from the womb:
“I am the Lord, who made all things,
    who alone stretched out the heavens,
    who spread out the earth by myself,
25 who frustrates the signs of liars
    and makes fools of diviners,
who turns wise men back
    and makes their knowledge foolish,

9. Isaiah 45:1 

The Lord says to his anointed Cyrus....

So this tells us who God is talking to.  

10. Isaiah 45:5

I am the Lord, and there is no other,
    besides me there is no God;

11.  Isaiah 46:6 

that people may know, from the rising of the sun
    and from the west, that there is none besides me;
    I am the Lord, and there is no other.

12.  Then we get to Isaiah 45:7 

I form light and create darkness;
    I make well-being and create calamity;
    I am the Lord, who does all these things.

13.  Isaiah 45:16, 

The makers of idols go in confusion together.

14. Isaiah 45:20(b)

They have no knowledge
    who carry about their wooden idols,
and keep on praying to a god
    that cannot save.

14.  Isaiah 45:16, 

The makers of idols go in confusion together.

I5. Isaiah 45:22

Turn and be saved, all the ends of the earth. For 

I am God, and there is no other. 

16.  Isaiah 46:6

Those who lavish gold from the purse, and weigh out silver in the scales, hire a goldsmith, and he makes it into a god; then they fall down and worship. 

17.  Isaiah 48: 3

The former things I declared of old;
    they went out from my mouth, and I announced them;
    then suddenly I did them, and they came to pass.

 18.  Isaiah 48:5

I declared them to you from of old,
    before they came to pass I announced them to you,
lest you should say, ‘My idol did them,
    my carved image and my metal image commanded them.’

So anyway, here is SOME of the context and key verses surrounding Isiaah 45:7 that I believe shed some light on what was meant by God creating evil.  

I believe the conversation God is having with King Cyrus in chapter 45 is telling him that there are no other gods.  The idols that are being worshiped are not causing the calamity that is happening in Israel, but rather is it God that is doing it.  

Some people believe that God didn't actually create destruction in Israel's lives, but rather that he took away His hand or hedge of protection.  But I personally believe God did create or cause calamity in their lives, and here are a few verses that I think speak to that.  

1.  Isaiah 42:25

So he [God} poured on him [Jacob/Isreal] the heat of his anger
    and the might of battle;

Plus other passages that I already quoted also:

2.Deuteronomy 28:63 (NLT)

 “Just as the Lord has found great pleasure in causing you to prosper and multiply, the Lord will find pleasure in destroying you. You will be torn from the land you are about to enter and occupy.

3. Joshua 23:15

But just as all the good things that the LORD your God promised concerning you have been fulfilled for you, so the LORD will BRING upon you the EVIL things until he has destroyed you from off this good land the that the LORD has given you."

4. Joshua 24:20

If you forsake the LORD and serve foreign gods, then he will turn and do you HARM, and consume you, after having done good."

I believe these passages tells us that it was in fact God that brought the evil and destruction on Israel and Judah.  Not only that, but  I believe He took PLEASURE in doing it.   As Barry mentioned in the article above, it was because of the covenant of judment He had with Israel, and what they agreed to.  We are now redeemed from these curses, as talked about in Galatians 3:13 " Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree"

So Jesus became the curse for us when He hung on the cross, so we don't have to worry anymore about God placing judgment on us, or causing destruction in our lives.  God is no longer imputing sin to us.

2 Corinthians 5:17-21

This means that anyone who belongs to Christ has become a new person. The old life is gone; a new life has begun!

18 And all of this is a gift from God, who brought us back to himself through Christ. And God has given us this task of reconciling people to him. 19 For God was in Christ, reconciling the world to himself, no longer counting people’s sins against them. And he gave us this wonderful message of reconciliation. 20 So we are Christ’s ambassadors; God is making his appeal through us. We speak for Christ when we plead, “Come back to God!” 21 For God made Christ, who never sinned, to be the offering for our sin,[e] so that we could be made right with God through Christ.