Error Reading Group File - trying to copy and paste an MCU from one group and adding it to the map someone else

[DD_Friar]

Salute

I wonder if anyone can advise.

I have just started getting the attached error when I try copy copy a MCU from a group to another location on the map.

I have tried re-saving the groups and also the editor reset .cmd

 

[DD_Friar]

Update - getting the same error when I create a new MCU template group. Other, older MCU template groups are ok?