This Problem can occur in a cluster or standalone.
version sql 2005 / 2008
in one of my environments, one of the nodes
successfully takes the clustered sql instance XY
and accepts pipe connections via management studio
and sql client hosts,
but not via tcp, e.g. named instance.
i find out that sql browser service does not start,
also in clustered infrastructure client based,
not controlled by cluster and set to auto...
by starting i got the error:
The configuration of the SQL instance MSSQLSERVER is not valid change instance
and that´s true.
my instance is not the default one.
also you can see, that under sql network configuration,
there are multiple instances registrated..
Cause:
Sometimes the first installation was not possible
or you removed an instance,
however sql browser service is not bind correctly to the actual used instance(s).
so, look at the registry with regedit on the failed node.
directly under
machine \ software \ microsoft \ Microsoft SQL Server
you find a key called "InstalledInstances".
If there are multiple Entries/Data,
delete the fauled instances.
SQLBrowser Service cannot bring tcp online by failed/missing instances.
i believe that sql browser is always taking tha last instance in the data field,
so cannot provide tcp port 1433 to the first instances...
close registry, start sql browser again and it will function...
also you can see, that under sql network configuration,
the deleted instance is away...