These look like errors on the individual problems, not an error in the library browser as a whole. You can check by including these problems in a practice homework set and viewing the problems there. Since they are presented one at a time it is clearer which question is causing the problem. Trying to debug questions while viewing them through the library browser can sometimes be problematic since there are a lot of special tricks that have been used to render the questions when they are not in a homework set. It usually works, but not always.
There is an outside chance that there is an error in one of the macro files. If you have your own site you should make sure that the NationalProblemLibrary is up-to-date. (Type svn update in the directory NationalProblemLibrary)
It's possible that there are some errors that have since been fixed.
Hope this helps and welcome to WeBWorK. Please post again if this doesn't solve your issues.
-- Mike