Upgrade fails with ORA-202 ORA-27086

I have a four node RAC cluster on Sun Solaris 10. The clusterware software is Oracle Grid Infrastructure 11.2.0.3. The only database on this cluster is currently Oracle 10.2.0.4. I am attempting to upgrade the database to Oracle EE 11.2.0.3. When I use the DBUA to upgrade the database, it never gets past the pre-setup steps and it fails with the following:
ORA-27086 skgfglk: unable to lock file already in use

The files that cannot be locked are the control files.

I double checked to make sure nothing was running on any of the nodes that could have held a lock on the control files. I used the fuser command on all nodes to verify that no processes were holding file locks on any of the control files. So I'm stumped why the DBUA could not proceed with the database upgrade.