The following errors are seen in compare server log (desvr) log when compare errors out:
desvr 2015-07-28 21:08:54.876094 32333 1092557120  Oracle Error 1756: ORA-01756: quoted string not properly terminated
desvr 2015-07-28 21:08:54.876094 32333 1092557120 
desvr 2015-07-28 21:08:54.876598 32333 1092557120  Error 1756 calling OCIStmtPrepare
In our example, there was a typo in the compare command's WHERE clause. One extra quote was put as seen below:
repair OWNER.TABLE_NAME where "'field_name > to_date('19-JUL-2015','DD-MON-YYY')". This resulted in:Oracle Error 1756: ORA-01756: quoted string not properly terminated.
The error can also occur due to other syntax errors in compare command, especially the WHERE clause
To resolve it, correct the syntax error and re-issue the compare.