I have a couple of questions if I may ask?
Were you trying to rename the designs directly after importing them (i.e. in the same session without a restart)?
How big are the designs?
My reason for asking is that it could be down to memory usage, if you have imported several large designs and the amount of memory allocated to the tool is quite low (I think the default is 512m) then it could be down to the fact that the tool was low on memory after the import.
Yes I imported them and directly renamed them.
There are two designs one is a small vehicle and the other is a medium sized vehicle, they are both full vehciles so will have approximately 700-1100 wires each so I'd say they were a reasonable size.