Tolerance boxes greyed out or missing

Hi All,

When applying tolerances to dimensions, if I select Symmetric the box is greyed out so I can't enter a value.  When I select Plus-Minus only one box appears for the minus value.

This problem has just appeared and is present if I try to alter the tolerance on the model or the drawing.  I have Creo 5 and 11 installed on my PC and the problem is present in both versions even though they read different config files.  When My Colleague opens the files on his PC the problem isn't present. 

Symmetric selected:

Plus-Minus selected:

Any help greatly appreciated!

Kind regards,

Clive