Does the log file report any errors?
On the mapping definition screen, try to add a filter on your input data and test the filter to check if you still receive data with your connection.
This is the error in the log
"There are no objects in the database to Import or the datasource could not be accessed. Make sure the datasource is not locked by another application or another user"
From what sort of data would you like to import data ? If it is from an Excel Worksheet check that your worksheet is not already open by other people or other application.
Fixed. The account used for the 'data connector' had been disabled and hadn't been notified.