I just encountered this error when trying to launch the game : an error window saying something like "Not enough storage to perform the operation", and the game doesn't launch.

If you encounter the same issue and are on Windows 7 like me, check if you have the file gameux.dll
in both folders "C:\Windows\System32\" and "C:\Windows\SysWOW64".
If you miss one, this is probably the issue.

I was in this case because I previously had issues with gameux.dll (See here ), and so did a bakup of the file and renamed it to make it ineffective.
So I had to rename it correctly. (and followed instead this way to make it ineffective: better solution )

Hope this may help someone who had the same issue :)

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tldr : if you have the error message "Not enough storage to perform the operation" when trying to launch Just Cause 2 and are on Win7, check if you have the file gameux.dll in both folders "C:\Windows\System32\" and "C:\Windows\SysWOW64" because the game need them both.
And beware of suspicious files on the web !