I don't think they are useless... but then again, I may be biased. The problem is that experience has taught 'us' computer support people that 999.999 of the 1.000.000 times the problems reported are somehow caused by the PC of the user..... and sometimes .... .... even by the users themselves.
No matter how friendly and patient and supportive one may be, if there's a problem at the other end then that's where it needs to be solved.
Now, your problem seems to be indeed a VERY strange one. It sounds like you indeed have run into some browser error and haven't cleared your cache. Then the error keeps coming back and back and back ...
First of all, do you have a customer account on simMarket already?
Which browser and version are you using, which OS, what version? Which anti-virus and anti-spamming software do you use? What ISP do you have? Any routers with non0standard internet protection settings? Any.... ... Norton software installed?
Oh, and when was the last time you re-installed Windows on your PC?
There WILL be a simple and logical explanation for your problem, but finding it may not be the simplest thing on earth ;-)