connection string to SQL named instance cluster within web.config suddenly stops working

web.config connection string to SQL named instance on cluster works for some time and suddenly stops working. I do the stops > start of app pool and it is working again, but after some time (of inactivity) it stops working!!!
Nothing is recorded in SQL profiler. SQL ports are dynamic.
Yes there is firewall between my server but it should not be issue as I'm able to access instance once I restart app pool.
Any ideas?

0 answers