Does it operate the smae way AFTER you format the column into a DATE?
If it does, then Yes You have a hacked up load of excel, get an update or get your money back!
I am at a loss, as it is more then one possible cause. You have have already looked at the requirements and compatabilites, so that isn't it.
Maybe missing a library build because of 32/64 bit? Try to run in compatibilty mode?