WCF Exception in IIS Only (“The underlying provider failed on Open”) – Access to Entity Framework

What if you try to run your WCF Service in IIS and get the following error although you have already done this post?

The underlying provider failed on Open.

For my case, it only happens when deploying to IIS 7.5. Everything runs perfectly fine in local (under Visual Studio 2008). This is .Net framework 3.5. The WCF Service is accessing Entity Framework on back end.

Well, check on the firewall rules. The following ports are being dropped:

MSSQL Monitor (Revolver) – Port 1434 (UDP)
Microsoft-DS Active Directory – Port 445 (TCP)

These ports need to be in white-list for Entity Framework communication between source (web server) and destination (database server).

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