Other Strange behavior with RandomAccessfile

This code works:

Dim iss As InputStream
iss=File.OpenInput (File.DirAssets,fname)
Dim bb(1024) As Byte
iss.ReadBytes (bb,23,4)

This does not work, "File not found":

Dim raf As RandomAccessFile
' Error in the following line
raf.initialize (File.DirAssets,fname,True)

i=raf.ReadInt (23)

Why? The variable fname is the same, I controlled also uppercase letters.