Help

I have been playing BG2 and finally installed the Throne of Bhaal add on disk.
I did a Full install from the disk. When I try to load ToB or access the watchers keep addin from within my current game I get a message " NO EXPANSION DISK IN DRIVE" THE DISK IS IN THE DRIVE!!!!!!!!

Ejecting the disk and reinserting it doesn't fix the problem as it still can't see it.

Uninstalling and reinstalling didn't fix the problem.
( Min install of Tob didn't fix problem).

Interestingly
Loading from desktop; if I don't thve the disk in the drive it asks for it to be loaded. I load it and it gets as far as the screen where you select SofA or ToB. If I select TofB it them wants the disk put in the drive(WHICH I HAVN'T REMOVED)

Why can't it see it when it has only just loaded the introscreen from it???????

Any ideas.
Whould a crack patch work to bypass the disk checking feature? Anyone got one?
I shouldn't neeed a crack program to run this as its a legimate copy.

Thanks