I had this little problem after downloading and installing the bot_moscommentV1.0.zip and com_moscommentV1.0.zip for Mambo 4.6.2.
Essentially no new comments would be saved, and trying to create one in the admin panel caused an SQL error.
After reading the SQL error and checking the mos_comment table in my Mambo database, I realised that SQL was trying to add a value to the "comments" field, but the table showed this field was called "comment" (no 's').
I used my SQL admin web page to access the Mambo database, and the mos_comment table, and then changed the name of the field to "comments".
This fixed the problem without incident.Please note however, that I DID backup the mambo installation using the xampp backup command BEFORE doing any changes!!!