Why does an SQL Server instance become unavailable on the network?

I have an occasional issue with connecting my VB.net database program to a server on the network using connection strings. Usually it works just fine, but every so often the customer(s) complain that the program won't connect. Not because I have changed the connection string or anything - which I haven't - but because of some unspecified or automatic change or update possibly to the customer's server's firewall, anti-virus etc.

Usually we fiddle with administrator levels, permissions etc. until connection is re-achieved. Is there some way we can 'future-proof' the connection between program and SQL Server so it doesn't fall over when there's a Windows update or etc?

Customers SQL Server version is 10.50.

Any pointers or suggestions welcome. Thank you.

You need to stop automatic updates to the server and firewall. Updates to those components need to be controlled, regression tested and scheduled for off-hours deployment.

To know more how to fix the issue:

SQL Server instance become unavailable on the network.

follow this one Enable Remote Connection on SQL Server 2008 Express - Linglom.com