>>What is DataFolder?
>>variable or hardcoded path to Data?
>
>It is a variable and I test it within the SP which points to the right folder. In fact, I can read the values from the tables all right. So the table must be opening in the right folder. The problem is that no values are not being written to the table and no new records are inserted. And no error message. Although error message is a moot point since it is hard to trap error in a stored procedure.

OK, try this:

LOCAL lcOldPath
lcOldPath = SET([PATH])
SET PATH TO
WAIT WINDOW FILE([MyTable.DBF]) && Just to make sure you open table in m.DataFolder
TRY
   USE (m.DataFolder + "mytable") IN 0 ALIAS MYTABLE AGAIN SHARED
   INSERT INTO MyTable (MyField) VALUES ([ABC])
CATCH TO oExcpt
   MessageBox([Error happened ]+oExcpt.Message)
ENDTRY
USE IN MyTable
SET PATH TO (lcOldPath)