I had the same Error 8003 on my level when light mapping..
I had just added a new EBE structure to a complex level with other EBE's and done the light-map..
No longer able to run level..(error 8003)
I then remembered I had changed something in the setup.ini file
I had increased the size used by entity shadows... after seeing a post by Preben to someone about
getting better quality shadows..
I went and put the value back to 512 in setup.. and re-lightmapped... level was working again...
I am in the Beta versions... so a little later a newer beta version caused the error to reappear..
but then another quick beta release had solved this before I was able to report it..
so if you are using the non-beta version then I think you should not worry..