This is more informational for other's use than a question:-
I spent quite a bit of time recently troubleshooting a problem I was having with DPM 2012 R2 Cumulative Update 9 on Server 2012 R2 with tape backup failures on our Dell TL4000. This started happening out of the blue and gave us the error message in DPM:
The operation failed because of a protection agent failure. (ID 998 Details: The parameter is incorrect (0x80070057))
The tape jobs would run until they were almost done, transfer data and then fail with the error above. The tape would show 0.13MB of data every time.
The server I was backing up was an MS Server 2003 32bit server and as such using a very old DPM Agent, so this sent me on a bit of a wild goose chase thinking that may be the problem. Turns out 2003 has to use this version of the agent.
Everywhere I looked it referred to this error as a common bug in versions of DPM prior to DPM 2012 SP1 where it had been finally fixed. Nothing about it since about 2013.
So I tried, re-protecting the server, rebooting, running manual tape backups and updating tape drivers all to no avail. Finally I decided to do firmware updates to the Dell tape drives before finally reporting the problem to MS. Happily the firmware updates fixed the issue. So hopefully this will save someone else some of my pain