Move the error details to a different table.  That table could be keyed by the clustering key of this table plus perhaps a sequential error number.

This table should almost certainly be clustered on JobID first rather than identity.  If so, that could save one nonclustered index and perhaps drastically reduce overall overhead, depending on how joins/lookups are typically done.  Ridding your mind of the myth that "every table should be clustered by identity" could massively improve performance of your entire system.