How do I? – Solve the “Cannot use ‘partitionResolver’ unless the mode is ‘StateServer’ or ‘SQLServer’” error

OK, so I have an app deployed on a SharePoint server. It's a standard ASP.NET web app and it runs on port 80. Since SharePoint is now a good little ASP.NET citizen and behaves just like any other ASP.NET web app, the two should live together in peace right?
Apparently not… I kept getting this error when I clicked a link in SharePoint that links to the web app.

Server Error in '/SPSWebApp' Application.

Configuration Error

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.Parser Error Message: Cannot use 'partitionResolver' unless the mode is 'StateServer' or 'SQLServer'.Source Error:

Line 179:

Line 180:

Line 181:

Line 182:

Line 183:

Source File: C:\Inetpub\wwwroot\wss\VirtualDirectories\80\web.config    Line: 181

Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET Version:2.0.50727.210

Now, most newsgroups and blogs I found recommended installing the web app on a different port. Though that might work just dandy in a wide open environment, it won't work if all ports are blocked by default and only certain ports are opened by request. So that certainly did not seem like a good option to me.

After some digging around and trying different things, I finally managed to resolve the problem. As with most debugging issues, it's a very small fix. In fact, it totals only 26 characters to be sure. It's a small change to the web.config file of the web app in question. To resolve the problem, we just have to add the "partitionResolverType" to the "sessionState" key. Change the web.config from this:

To this:

partitionResolverType="" …

And viola! All working again! ;-)

Later
C