Cannot compose mail in Thai language

Dear Sir,
I've upgraded from Microsoft Office 2003 to Microsoft Office 2007
Enterprise. It works well except Microsoft Outlook 2007 as this mentioned
problem.
Problem :
I compose a new mail with Outlook 2007. When I type message in the
content section in English, it works well. But when I switch to Thai, I
cannot type anything unless I type some characters first e.g. "/". How can I
fix this problem ? Please help.
Environment : I've also set Thai Language in Editor options ->
Language Settings. And this problem never occurs in Microsoft Word 2007
OS : Windows Vista Business Edition

Best Regards,
FancyM