Adam,

The answer to this problem was removing the ConfigurationPath setting from the Editor - I had it set to a custom menubar file which worked with no problems under version 4, but version 5 doesn't seem to like it.

 

My setting was ~/CuteSoft_Client/CuteEditor/Configuration/AutoConfigure/SSFull_noCode.config

 

And it wasn't my custom menubar - as i copied it into one of the existing ones and used the AutoConfigure setting to reference it and this worked ok.