Action Message Entry Table cannot be locked

When we are executing the Requisition Worksheet, wich takes approximately 15 minutes to complete, other users get a message that 'The Action Message Entry Table cannot be locked or changed because it’s already locked by . For that reason we always execute it during lunchtime, but we want to do this during morning hours also. It seems weird to me that Navision doesn’t handle this in a more convenient way. I guess using a SQL database would solve the problem, but I don’t want that; our company is very small, we have only some 20 users. Does anyone have the same problems? And is this normal behavior in Navision Attain 3.00? Thanks for your reply. Michiel Hageman