IIS (ASP.NET application) with SQL going crazy!

I have a really strange problem.

I have an ASP.NET 2 c# application which on load access 2 stored procedures.
All work OK (normally)

The application has an ajax timer which every now and then calls the server.

Then at one point in time I get an error. On refresh I see that the stored
procedure is being called but it returns nothing (If I call it via SQL
Manager Studio passing same parameters it works well).

I press refresh, the first stored procedure works but the second fails
(returning no data but no exeception)

I press refresh, the first fails,

etc, etc.


Then I resart IIS and all works well (.... till system hangs again)


What's happening? And how I can go around it???


Evan