500 Server error on site. Event Message "A parser error has occurred"

Hi,
I'm new to this forum. I was directed here from an Expression Web forum.  I'm hoping maybe someone here can help me.  I am using Expression Web, but this seemed like the most appropriate place to post. 
I have a site (InWestmoreland.com) that uses masterpages and I'm having a problem...sometimes...when I publish the site.   There are times that when I publish the site, I get a 500 Server error.  When I look on the server, the error message contains:   Event code: 3006
Event message: A parser error has occurred.
Event time: 8/4/2010 6:00:57 PM
Event time (UTC): 8/4/2010 10:00:57 PM
Event ID: d92b79e9dc314dcb809f3a70dfbfd778
Event sequence: 62
Event occurrence: 9
Event detail code: 0   Further down in the error it gives Exception ...