strange chars created..

[Joy]

in the macros, we use DateFormat to change the format of date, and assign it
to Text1:
tsk.Text1= DateFormat(tsk.Start, pjDate_mm_dd_yyyy)

However, sometimes, strange invalid chracters are created:
11/18/ľୀ9ࠡ
which should be 11/18/2009

sometimes, we use import and export map to import and export data from and
to a csv file. and some invalid characters (not ASCII) are created for a
task's name, or some hidden fields which users may not modify.

I am not sure how it is created. does anyone give some idea and how to avoid
it?

thank you