There have been a couple of reports of this, but so far we have not been able to reproduce it to determine the exact cause. It is reasonably certain it is data related in some way. The exception report in your case suggests it happens when trying to sort Series information.
There is currently an issue raised for this at
http://calibre2opds.myjetbrains.com/.../issue/c2o-131. If you are prepared to let us have a copy of your metadata.db database so that I can try and reproduce it then please attach it to this issue (zipped if necessary to reduce size).