You will get this problem when there is an issue with the TACACS server. In this case you can disable the TACACS and use the local database.
Just in case you need to disable TACACS+ login module here are the steps:
1. stop the CW2000 daemon manager
win2k: net stop crmdmgtd
solaris: /etc/ini.t/dmgtd stop
2. go to NMSROOT/CSCOpx/www/classpath/com/cisco/nm/cmf/security/jaas
3. delete the file, JaasConfigModule
4. restart daemons manager
win2k: net start crmdmgtd
solaris: /etc/ini.t/dmgtd start
This will bring back the default login module which is "local".