Clearing the command queue in Security Commander (Prior to S.C. 2.x)
In Security Commander 2.0 and above there is a menu item within commander to do this.
The following command is entered from the CMD prompt, it IS case sensitive and the XXX's need to be replaced as per the legend below.
Press Ctrl C to exit the sqlcmd enviroment and return to the command prompt after running.
sqlcmd -S XXXXX\SPSQL -U sa -P XXXX -q "use alliance8300; delete from dbo.messagesbackup;"
-S insert your computer name, -S MyComputer\SPSQL
-P inserts your sa password, -P password
If run correctly your screen should look like the below image: