What name are you using when you atempt to connect to SQL Server running on a cluster> There is no functional difference between connectiong to a stand alone machine or connecting to SQL SErver running on a cluster. The only difference is that on a cluster you connect using the virtual SQL Server name instead of the machine name.
Are you using the virtual SQL Server name, the cluster name or the actual node name when you attempt to connect? Also in many instances clustered SQL Servers are named instances. If this is the case are you specifying the instance name when you attempt the connection.
If you know the ip address of the virtual SQL Server and the port number it is listening on, you cna attempt to connect using <ip address>,<port number>