Unable to enter Simulate mode

Hello, and congrats to all involved with XOD - it has enabled me to finally get into developing a few projects!

However, for the last two days I have been trying to use Simulate on a project but get the following error message:


Is this a problem with the system? I have checked the Forum etc, but there is no info that i can see.

EDIT 12/11/2020. I just tried Simulation on the currently deployed version of the project and it works fine, but again on running the slightly modified version I get the same error msg. Clearly something I have done upsets the compiler but there were no other errors reported. I will now drill down and investigate the mods.