Where, exactly, are you having problems?

Is it during the unpacking process?

For instance, if you download ABCoolStuff.zip and the zip decompressor gives you an error, that could be one of two things.

1) Your file is corrupted.
2) Your zip utility is not compatible with the format you're trying to decompress.

Solution:
a) Download the file again. 
b) Download the newest version of the decompression utility for the format you are trying to decompress. 

(WinRar is generally good as is 7-Zip and PkWare's "Winzip".  With those, you can handle just about any compressed archive file format commonly used.)

Note: There ARE some compatibility issues with compressing a file using one utility and decompressing it with another even using the same base format.  I've had problems decompressing .rar files simply due to the file being compressed under one version release and it not being compatible with another across two different programs.

If you are having problems actually using the files in your application, then that's a different issue and you should probably try to PM/email the creator.