No. of records that could not be converted: &

What causes this issue?

The number behind the message text indicates how many records in the
current data packet could not be converted due to a technical error.
The type of error, information on possible causes, and the necessary
activities for error recovery can be found in the error messages above
the current statistics.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.