> My question now is: Can some body help me figure out
> why such a "exclusive" access (as mentioned in the KB)
> is required?

Because adding a FK will raise an error if it isn't an exclusive
connection.

With regards,

Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL
Server.
Upscene Productions
http://www.upscene.com