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Welcome to SitePoint!
Without any code shown, there's little chance that anyone here would be able to definitively tell what's happened. Anything from an incorrect format upload to a server problem to a coding problem. More info, better chance to decipher the problem.
Is the image in question particularly large?
Make sure you have enough memory to process the image. If it is large, the image handling functions can eat up a lot of memory. But, like dklynn said, it could be anything.
Where is the link for your code?
Why would you ask for a link to the code after 2 years? This person only made 1 post and has obviously completely forgot this place exists.