Intraweb DataModule multi users

Today after I deployed my Intraweb application, global variables that has been declared in public section of DataModule is shared. When user 1 modified a variable, user 2 will get this new modifications. Then I removed these variables to UserSession and it works fine. But I get the same problem with tables, I put a lot of tables, queries and StoredProcs in DataModule.
I noticed that when two concurrent queries has been called for the same database component I get some times error like "can not perform this operation in a closed dataset"
Does any one encounter such problem, and what is the solution

I use MultiThread in ServerControl's ComInitialization property