Hi Arshiya
please check the MDS log first, get the SQL statement error as Carlos mensioned above.
you can read this log from console ,and also you can get the source csv file from bellowing path in your MDM server: <drive>:\usr\sap\<SAPSID>\MDS00\log, get the right time log file and you can open this file with SAP MDM Logviewer, there find the error statement.then we can go further.
best regards
Stephen