While uploading data file from m340 plc I am getting message "old *.DAT file cannot be restored"

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You can store ( Export) the value of the following data in a file ( .DAT & .DTX )
boolean-type located data: %Mi
word-type located data: %MWi
unlocated variables
function block instances

*.DAT:
Saving PLC data to a *.DAT file is allowed for all previous data types. *.DAT contains only data blocks.
Restoring all data blocks from a *.DAT file to the PLC is allowed if the project has not been built since the Save was done.If a build was done, only BOOL and WORD located data (%Mi and %MWi) are restored.

*.DTX (requires Unity Pro 6.0 of higher):
Saving PLC data to a *.DTX file is allowed for all previous data types. In addition, application references (at the time of the Save) are saved.
Restoring data from a *.DTX file is allowed even if the application has been built and/or data has been modified since the Save was done. Compatibility Rules for Restore Using a *.DTX File explains the restoration process and the types of data that cannot be restored.