We have a SQL 2008 Cluster (A/A/P) that's been in place for years, and today one user reported that he could no longer connect to any of the Instances using SSMS 2008 or SSMS 2012. No other users are reporting this issue, and I'm able to connect to the server and instance without issue (example Server1\Inst1) as are other users. The work around for him was to use the Port instead (Server1,12001), but I'm scratching my head on why this is occurring. He's able to connect to all of our other SQL servers by instance outside of the cluster, but each of the instances on the SQL 2008 cluster are doing this for only him.
My hope is this is just something on his machine, but my fear is it's the first drop of a much larger problem. At this point I'm still investigating, so any suggestions on what could cause this?