Caché problems

Hello,

My site (for a long time) is experimenting a lot of problems with the cache. The site is made in Joomla with Cobalt 8. The programmer who built the site can not find an answer (more I think he is not doing anything at all for a long time, but this is another issue) Since we decided to improve the site with cobalt 8 and move to joomla 3 the problems with the cache came up. I have been talking with the staff working in the company I host the server but they say it is not a server problem at all. As it is an e-learning site the main problems I founding are:

• Students report to that lessons get suddenly vanished (but we can see them..)
• They can not get out from the site (they experiment an extrange loop that does not allow them to disconnect from the site)
• After a while without activity at the site and if you want to move to another page (still logged) it appears a little robot at the top of the site saying Upps the resource can not be found or something similar.

And some other problems I can not exactly remember now.

Can you help me please?

Thanks