I'm rather late participating in this thread (new to the forum) but thought I'd add my $0.02 as this is a commonplace issue and some hints might help others having the same problem. Although it's not possible to say for sure what your particular problem might be, perhaps a few tips might help.

As Wildhoney asks above, your extension_dir configuration directive is likely not pointing to the correct location, which should be to the ext directory found in your PHP installation directory. If this is the case, PHP won't be able to find the gd2 DLL.

However, given the nature of this particular error (imagecreatetruecolor does not exist) I'd speculate there's some DLL mixup on your system, and you have the GD DLL installed rather than the GD2 DLL. I bring this up because the imagecreatetruecolor functions are not found in the GD1 DLL. Check your PHP installation's ext directory to see which version you have.

Hope this helps,
Jason

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