Just a point note, the above query only shows errors in the last 5 minutes. You have to change it to check for one outside that period.

If you find the error is an update against a row you don't have its likely your the subscriber table is out of sync with the publisher.

There a couple things I can think of

-The table is out of sync and missing rows

-The sp_msins_<table> proc has been edited and is failing to insert

Its unlikely the publisher is failing to send new rows to you as this tech is proven to work. There must be a breakdown somewhere.