From the Misc/Setup pull-down menu, choose Company/Misc Info to access the Company Setup screen.
Right-click on the reddish-colored text there that says Company Setup, and choose the View Technical Program Defaults tab option.
Now in the grid you will see, scroll down to probably near the very bottom, and look for a Variable Name of "WarnAboutContactBalanceFlag". Change the Value for it to be 0 instead of -1, and after making the change, hit the up arrow on your keyboard to move to a previous row, which saves the change to the record you were on, and then click OK.