This error you are getting has lots of possibilities. Is your file has text qualifier??

If yes then you might have " " empty space in between and your destination column data type is integer.

SSIS cant process " " empty space as an int. you need to convert it as null and then process it as int.

Second possibility is Column Delimiter.

You are getting this error because of Column Delimiter.

I had the same issue. Open your file in notepad++ check your column delimiter and change accordingly in flat file connection.