I've created my own Startup file to be used that calls
cseg at 0
if the modified startup does not have the entry label and exit call you will get "startup missing" in commandline mode. I guess in the IDE mode that would make the standard get included. I imagine this is the part required:
?C_C51STARTUP SEGMENT CODE CSEG AT 0 ?C_STARTUP: ljmp ?C_START end
Ok. Thank you. I was missing a small part of that.