REpeated extension/profile corruption

Hi,
I've been having a problem adding extensions. I get the -203 unexplained error at the end of each .xpi download. I've tried removing PFF, reinstalling and the same thing happens. I've tried it with regular FF and the same thing is happening. I know it's not incompatability with the extensions since my laptop has the same ones I'm trying to load and runs fine.

with each new installation I can usually load one to three extensions and then it starts giving the -203 error. I've tried removing the extensions.ini, cahce and rdf files, both while FF was running and when it was closed. No luck.

I also have Tbird running and have no problems there (just fyi since it alos uses extensions).

Unfortunately I'm assuming this is some sort of hardware/software configuration issue unique to this PC but I thought I would check to see if anyone had any suggestions on fixes?

Thanks