Error message


New member
I just started receiveing the following error message in Surveyor and it now pops up every one in a while. I click on 'continue' and all appears OK:
Thread Exception ER NullReference, line 1326, file

Stack dump

Function $Permit{} Train:: TakePermitOnTrack (bool), line-1
Function $avoid$ Train::Init(), line 1397

I would appreciate it if someone could tell me what this means.
Thanks in advance.