when i selected an edge or a face ,an exception occurs

I have installed OCC6.5.1,a exception puzzled me for a few days.
1. In the project Viewer3d,I have created a box,but the exception will occur when the cursor meets with the box.The exception is "Viewer3d.exe in 0x0aa6244b at the unhandled exception: 0xC0000005: read access violation occurs when the location 0x00000000".
2. The same exception also occured in my own program which everything works well under OpenCASCADE 6.3.
3. The enviroment variables I have setted are:
VCVER=vc8
OS_TYPE=win32
CASROOT=C:\OpenCASCADE6.5.1\ros
Add to path:
%CASROOT%\win32\vc8\bin;%CASROOT%\..\3rdparty\win32\tcltk\bin;%CASROOT%\..\3rdparty\win32\tbb\bin;%CASROOT%\..\3rdparty\win32\gl2ps\bin;%CASROOT%\..\3rdparty\win32\ftgl\bin;%CASROOT%\..\3rdparty\win32\freeimage\bin;
CSF_LANGUAGE=us
MMGT_CLEAR=1
CSF_EXCEPTION_PROMPT=1
CSF_MDTVFontDirectory=%CASROOT%\src\FontMFT
CSF_MDTVTexturesDirectory=%CASROOT%\src\Textures
CSF_UnitsDefinition=%CASROOT%\src\UnitsAPI\Units.dat
CSF_UnitsLexicon=%CASROOT%\src\UnitsAPI\Lexi_Expr.dat
CSF_SHMessage=%CASROOT%\src\SHMessage
CSF_XSMessage=%CASROOT%\src\XSMessage
CSF_StandardDefaults=%CASROOT%\src\StdResource
CSF_PluginDefaults=%CASROOT%\src\StdResource
CSF_XCAFDefaults=%CASROOT%\src\StdResource
CSF_GraphicShr=%CASROOT%\win32\vc8\bin\TKOpenGl.dll
CSF_IGESDefaults=%CASROOT%\src\XSTEPResource
CSF_STEPDefaults=%CASROOT%\src\XSTEPResource
CSF_MIGRATION_TYPES=%CASROOT%\src\StdResource\MigrationSheet.txt