We just just installed a Viking E-20 and the content in this thread still worked great. Local username, digest username, and password all need to match the DN you create for the SIP device. Use that DN in the username/pw field of the Viking IP Prog...
TAC confirmed the bug and added my case to the list. I confirmed with them it exists in 10.5.4 as well. For now, 10.5.1 is the most current working version which is their workaround.
Thanks for your reply Aaron. Actually just came across this bug which is matching my experience and specific to 10.5.2. It was just updated on Friday. I'm opening a case so that I can be added to this reference. Bug CSCus34828