CitectSCADA Override

Hi, 

 i am using Citectscada ver7.5 for a HMI on one of our production machines. i have found that a variable tag is in an incorrect state due to a sensor/coms fault. When i try to put the tag into override mode it is unavailable/greyed out when i right click on the tag. Does anyone know how to resolve this please? 

i currently have no access to the PLC or electrical drawings to diagnose the faulty sensor etc though its alarming for a part of the machine which i no longer use so i would like to override the state. 

thanks in advance, 

Ed