You should use "perl -MBit::Vector=100 -e 1" to check for the availability of this (or similarly of any other) module; this will give an error message all the time (if the version number of the installed module is not higher than 100, as in this example - I usually just use "10") and will inform you which version is installed, if any. There are known issues with MacOS X and my module in previous versions. These should be fixed now. Please let me know if not.