When you use Private data session you must be sure the tables are NOT opened Exclusive.
Also it is a good idea to check for errors in that function and return if you succeed to open the file, i.e.

FUNCTION UseFile(filename)

   LOCAL lbReVtal
   m.lbReVtal = .t.
   TRY
      IF NOT USED(filename)
         USE (filename) SHARED IN 0
      ENDIF
      SELECT (filename)
      SET FILTER TO
      SET ORDER TO
      SET RELATION TO
   CATCH 
       m.lbReVtal = .f.
   ENDTRY

RETURN m.lbReVtal

This is of course very generic error handling, you could extend it.




>i am runing this software on single machine.
>i am using a procedure file to use my dbf files like below :
>
>procedure usefile
>****
>para filename
>if !used(filename)
> sele 0
> use (filename) excl
>endif
>sele filename
>set filt to
>set order to
>set rela to
>******
>
>some files i used in my main.prg
>like :
>=usefile("customer")
>
>now i changed my form datasession to private and using the command to
>open my dbf files in load event of form
>like :
>=usefile("customer")
>
>error "file is in use"
>
>please help me
>
>warm regards,
>mk.