Im using access as database. I don't know which page cause the problem. When 2 visitors visite my site, surfing from category to another category or from product to product. The problem occure, only part of the site load. The content connect to database can't show. But this problem is gone, once 1 of the visitor left or stop playing my site.

I had an issue similar to this once and found that if I used the cache attribute on my query tags it cleared up the problem.

This depends alot on what language you're coding in and what specific error is appearing - can you clarify those two points?

get rid of access and use mysql

access should handle it but i tends to be unpredictable. I'd also assume part of the problem could be in your code