OperationalError is not defined unless you have the mysql module installed. You can test this on obelix. Please also test "create" you do no have a database.

$ pegasus-db-admin update
Traceback (most recent call last):
File "/data/scratch/rynge/pegasus/pegasus-4.5.0cvs/bin/pegasus-db-admin", line 37, in <module>
main()
File "/data/scratch/rynge/pegasus/pegasus-4.5.0cvs/lib/python2.7/dist-packages/Pegasus/db/admin/commands.py", line 226, in main
DBAdminCommand().main()
File "/data/scratch/rynge/pegasus/pegasus-4.5.0cvs/lib/python2.7/dist-packages/Pegasus/command.py", line 104, in main
cmd.main(args)
File "/data/scratch/rynge/pegasus/pegasus-4.5.0cvs/lib/python2.7/dist-packages/Pegasus/command.py", line 23, in main
self.run()
File "/data/scratch/rynge/pegasus/pegasus-4.5.0cvs/lib/python2.7/dist-packages/Pegasus/db/admin/commands.py", line 103, in run
db = connection.connect(dburi)
File "/data/scratch/rynge/pegasus/pegasus-4.5.0cvs/lib/python2.7/dist-packages/Pegasus/db/connection.py", line 50, in connect
db_create(dburi, engine)
File "/data/scratch/rynge/pegasus/pegasus-4.5.0cvs/lib/python2.7/dist-packages/Pegasus/db/admin/admin_loader.py", line 83, in db_create
except OperationalError, e:
NameError: global name 'OperationalError' is not defined