For 5.6 i had 32 bit db2 client, now along with Toad 6.0 i have removed 32 bit and installed 64 bit db2 client - no special configuration in db2cli.ini, AutoCommit is ON and in toad options i have “Use individual connection for each open editor” OFF(unchecked).
You can try to reproduce error like this:
Start Toad, connect, open few editors with sql and execute them. Then don’t use Toad for min 30- 60 min, and then try to run sql from last opened editor. You should see background process for sql running and then, because closed connection, error from screenshot appears.
When you close the window with error message, Toad will reconnected again end queries can be executed normally.