Crystal Report Issue

Hello All,

I have implemented one application in visual studio 2010.
In application, there are almost 50+ crystal reports.
Issue is, while client is using system on daily basis, reports are working fine.
But after sometime, reports get blocked and not display in front end.
Shows crystal report loading error.
Then we need to restart IIS and then it starts working again.

Can you please help to to resolve this issue permanently.