Are you talking about Zap?
Does the error prevent you from loading the file? Or does it load it and
then just not display any symbols?
I'm guessing that it uses _stext to know where to start debugging.
If it does successfully load you may just need to do what the message
"set PC to entry point"
You can view the registers and modify them in Zap. Modify the program counter to where your reset vectors to.
I'm assuming your loading an H12 record or some kind of elf file.
Try loading it as a S19 file, I know Zap supports um, and since they
don't have any symbols I don't know how it could stop you.
You would of course lose your source level debugging, but you can
redefine symbols after you get all the bugs worked out .