No idea about the specifics, but it is just a cache file.
Move it somewhere (so that you've got a copy for posterity) and run
Backups are advisable because I hacked my tagtime files long ago, and this may not be the official answer…
But I am confident in the "It's just a cache file" part. Your TagTime log file and your Beeminder goal are the master sources, the cache just saves having to examine the whole of history after every ping.