Could not connect to named instance anymore via Management Studio but SSIS works

Hi,

I have a connectivity problem with my SQL Server: I have two SQL servers installed. (Named and default instance)

I could connect to both servers and work with them. Then I installed App fabric cache and deployed a website on the same machine.  Normally this works fine, but on this installation I am not able to connect to my named instance anymore.

I get the following error code: provider: SQL Network Interfaces, error: 26 (http://www.microsoft.com/products/ee/transform.aspx?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=-1)

I already tried the hints provided by this page:http://blogs.msdn.com/b/sql_protocols/archive/2008/04/30/steps-to-troubleshoot-connectivity-issues.aspxbut I didn’t get it up and running again.

Strange is also that I can run my integration services packages on this named instance via VS Data Tools but not via a SQL connection via C#.

Any ideas how can further investigate this issue?

Thanks

Yvett