I learned that Zip sometimes behave unexspected. From time to time we recieve Zip files which i am unable to open with the MacOS X 10.5.2 built in engine. The feeware "The Unarchiver" helps me because it proceeds regardless of an error. Maybe its Apples part to change the OS engine.
MacPro 8 Core 3.2 GHz, 16 GB RAM, 4 TB HD. XPress 8