Unless this is relevant (from B5500 Release Notes):
5500.10 Fixed issue with SD cards on Dell D420 and D430On Dell D420 and D430 laptops we have had an issue with our removable media encryption option and inserted SD Memory Cards. With the cards inserted and encryption set to encrypt all drives, the machines Status log always showed the error e0020009 "Unable to get disk partition info…". In addition to that the issue caused the encryption to fail on drive C. This has been fixed in this release.
Then assume disk started to fail. Perform disk diagnostic (surface scan or SMART analysis). Have backup up to date.
this is client v5.1.8. The machine has been encrypted for about two months, and the problem just started today. There are no external devices of any type plugged in except a USB mouse.
maybe they converted the disks from basic to dynamic?
Is that error permanent or intermittent. Did you check if anything else changed in that PC? Anyone turned on disk compression on whole C drive to free up some disk space? Root of C need to be uncompressed, all the rest can be.