I don't think this reading is "very high" -- it is only a little out of range. In fact the lower end of that range is an error and antiquated. Newer guidelines have 400 as the lowest normal. 211 is NOT normal and significant neurological symptoms may be present at 211.

There are some rare medical diseases that may increase B12.
Some overgrowth of bacteria in the bowel may do it.

Also some kidney disease may have it... this link gives readings for the various kidney problems:
http://www.ncbi.nlm.nih.gov/pmc/arti...00070-0064.pdf

If you look at the chart on page 2 you can see that the readings are inconsistent with several patients with the same problems.

B12 can be in some fortified cereals, and you may be getting it that way too.

Your doctor would be your best bet for further opinions.
However, many of us take supplements and have readings of 2000 with no problems. The FDA does not supply any toxic upper level for B12 as decades of experience have not found any danger with it.

An unexplained high level is not toxic, but may point to something else going on with you.