delphi dll problems !

Dear Experts,
I have a problem with a Delphi written DLL. At initialization, the DLL starts by opening a file of records. Within a loop, it should read each record and put its values into an array. It reads the first record without a problem. When it goes round the loop to read the next record, it gets the wrong values from the record.
When the program runs as a normal Delphi program the problem does not occur. However, when the same program is written as a DLL, the problem occurs.
Are there special rules for DLLs about reading files?
Here is the code where the problem occurs.

try
    AssignFile(FHash, DefaultHashFile);
    Reset(FHash);
    While not eof(FHash) do
   begin
         Read(FHash,ECell);
         //Convert Ecell WideChar array to a unicode string  /
        CharCount:= 1; S:= '';
        repeat
            S:= S+ ECell.Str[CharCount];
            Inc(CharCount);
        until  (ECell.Str[CharCount] =#0 ) or (CharCount >= 30);
          N:= Ecell.Location;
          NameIndex[N].Str:=  S;
        CharCount:= 1; S:= '';
        repeat
            S:= S+ ECell.Phono[CharCount];
            Inc(CharCount);
        until  (ECell.Phono[CharCount] =#0 ) or (CharCount >= 30);
         NameIndex[N].Phono:=  S;
         NameIndex[N].DiskStart:=  ECell.ArrayStart;
         NameIndex[N].DiskDivider:= ECell.ArrayMiddle;
         NameIndex[N].DiskTail:=  ECell.ArrayEnd;
         NameIndex[N].Eastern:= ECell.Eastern;
         NameIndex[N].AltMarked:= -1;
   end;
    Closefile(FHash);
  except
      DisplayMessage('error reading Main Index table contents');
      Closefile(FHash);
      Exit;
  end;