For example, if I put the correct answer to the problem:
it just posts some warning message and does not grade the problem at all.
The warning messages shown are:
PG question processing error messages
PG warning messages
The evaluated answer is not an answer hash : ||.
WeBWorK has encountered warnings while processing your request. If this occured when viewing a problem, it was likely caused by an error or ambiguity in that problem. Otherwise, it may indicate a problem with the WeBWorK system itself. If you are a student, report these warnings to your professor to have them corrected. If you are a professor, please consult the warning output below for more information.
Use of uninitialized value $new_rh_ans_evaluation_result in concatenation (.) or string at /opt/webwork/pg/lib/WeBWorK/PG/Translator.pm line 1337
Previously I was using version 2.11 and I had a similar problem albeit a different warning message.
So I upgraded webwork2, pg, libraries and MathJax to the latest version, and updated the database following http://webwork.maa.org/wiki/Release_notes_for_WeBWorK_2.12#Upgrade_Instructions, but the warning message did not get resolved.
It seems like all the problems using RationalExpEvaluator spits out this warning message. Any ideas?
Thank you in advance.