When I access certain websites (including parts of the Dell site) I get messages of the following type:

 

A run time error has occurred

Do you wish to debug?

Line 0   (line number varies from message to message)

Error: "Windows documentfrmDSNFeedback is null or not an object"  (Could be a lot of other messages, but they often end with "is null or not an object"  

 

Can anyone tell me where they are coming from (Javascript?), why they are happening, and how to stop them happening in future?  They are very annoying.   I read one knowledge-based article, but it seemed like a lot of work and no permanent solution - I hope the problem was different.