If I start rebuilding a series of existing personal books, just doing Edit/then Build, because I have updated a number of resources, after I get to about 6 or 7 of them I start getting errors. These errors seem to be because too much is going on. If I wait for all the existing builds to finish, then reopen the personal book tool,m they build fine. A picture:

I don't expect them all to build at once, but I should be able to start them!