Verify each credential type username/password is set for your devices under Profile > Troubleshooting features
What version of DSET is it running? Start > Program Files > DSET 3.3?
Usually the DSA logs will display a failure code like -1, -6,. -6 has to do with either the username/password or the IP address is not reachable. Can you check to see what errors are displayed in the following file?
C:\Program Files (x86)\Dell\Dell Integrated Support\logs\log-file.txt
Is there an SR# on the GUI for the failed DSET