Gettin an unexpected error when decompressing a ZIP archive, using internal mechanism build into Windows XP (and newer) Windows Explorer (i.e. by clicking archive with right mouse button or dragging it somewhere and using proper option from menu to decompress)? Then you can be 99,9% sure that such archive is simply password-protected and encrypted in the same time. Windows can't handle such archives. But, in the same time, it is stupid enough to throw you some idiotic, pointless, meaningless errors instead of simply saying, that i does not operate on encrypted archives! What a low...
As it was said -- Windows can't handle such archives. It is only able to handle standard (simple) password-protected archives, without encrytpion. Encrypted archives beside standard header (that is, why Windows correctly detects it as ZIP archive) have garbage in the file body (encryption) and this seems to be too much even for newest Windows Explorer on board Windows 7.
You need to use a bit more professional unzip client, like for example the one build into Total Commander, to handle ZIP archive in this case.