can not delete file

I am uploading a picture file using a 3rd party control which works fine.
I am then using some code resize the picture which works.
Then I am trying to delete the original file that I uploaded:

File.Delete(MapPath("./") + "EventPictures\" + strUploadedFileName)
I then get this error message:

The process cannot access the file because it is being used by another process.
Thanks for your help

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