Looks like you may have to wait a bit for the fix Clive,if this is the problem :
Microsoft Knowledge Base Article - 175361
OLEXP: IPF in Msconv97.dll Pasting Text into E-mail Message
The information in this article applies to:
Microsoft Outlook Express 4.0 for Windows NT 4.0
Microsoft Outlook Express 4.0 for Windows 95
This article was previously published under Q175361
SYMPTOMS
When you copy text from a program and then paste it into an Outlook Express e-mail message, you may receive the following error message:
MSIMN caused an invalid page fault in module MSCONV97.DLL at <address>
CAUSE
This problem can occur if the program you copied text from uses InfoViewer version 4.x. There is a problem in the font table of InfoViewer 4.x-based programs.
RESOLUTION
To work around this problem, follow these steps:
Paste the text you copied from the InfoViewer 4.x-based program into WordPad.
Copy the text from WordPad and then paste it into the Outlook Express e-mail message.
STATUS
Microsoft has confirmed this to be a problem in InfoViewer 4.x. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.
You'll just have to be patient and hope they fix it soon