One day a user can click on a hyperlink to a document (word, excel, one-note) in SharePoint and everything is great.
Next day the user gets an Internet Explorer error message or simply crashes trying to access the same document.
Cause (or at least my opinion on the cause):
The user computer has two versions of office documents, most likely 2003 and 2007. When office updates are applied (sometimes automatically if you have automatic updates on, or by SUS server pushes) the dll (OWSSUPP.DLL) is overwritten with incorrect information or is corrupted.
Easy actually, follow the instructions below...
Open Computer: C:\Program Files\Microsoft Office\Office12
Find and Delete (putting it in recycle bin) this dll: OWSSUPP.DLL
Run Office Diagnostics by: Start -> All Programs -> Microsoft Office -> Office Tools -> Microsoft Office Diagnostics -> Run the Diagnostics
When complete, close Diagnostics and attempt to access a task list or open a document within SharePoint Portal.
This should fix the issue. Good luck.