We seem to get this problem pretty often.  It's not repeatable 100% of the time, but both me and a coworker of mine get it frequently.  If we're in a screen somewhere (nowhere specific) and hit the ESC key pretty quickly to back out all the way, it will work, but then we can't click on any menu items.  We get the following error:
 
"Access violation at address 006E9A43 in module 'Tp5wdba.exe'.  Read of address 00000458."
 
Clicking OK will repeat the error once.  Closing DBA after this gets us:
 
"Exception EAccessViolation in module Tp5wdba.exe at 002E9A43.  Access violation at address 006E9A43 in module 'Tp5wdba.exe'.  Read of address 00000458."
 
 
 
DBA Classic 2004.1 w/ ISTS 05/17/11.