Sounds suspicious. Again I'd assume a different program (most likely some firewall/antivir/antispy) program interfears when a zipfile operation is performed and locks the file, so cmpro's packing/unpacking fails in that moment.
Another possibility is that existing files were bad in the first place (though then it would always fail). You can turn on Settings->Compressor settings->full zip structure scan. This is activates additional zip strucuture test (but is a bit slower).
But as you also got problems when checking the cmpro version ('is used by a different..') I really think some other task is interfearing.
Would be interesting to know which virusscanner or firewall you're using.
For testing purposes: Turn all other running background tasks off.
