RSS Feeds - Why would it be timing out?

[Sheffielder]

I have two invision boards on two entirely separate sites on the same server

Both are sending out RSS updates and I can see in the feeds that all the latest posts are there

BUT

If you put the RSS feed address into a URL bar one comes up immediately, and the other site times out when you check that one 

This is causing my social feed via DLVR.It to not be sending out any social updates at all on twitter or facebook

Any ideas why the RSS feed would not be appearing instantly in a browser when you put the address in?

[Sheffielder]

Hmmmm this is so weird

I deleted the RSS feed in question that was giving me grief, then created a brand new feed that contained every forum and subforum and it worked fine

Then went in to edit it to show only the forums that I want non members to see and again it starts timing out?!