Hi Randy,
As of 10.2.0, bigd no longer appends any CRLF's to the monitor send string so this should work if you are on 10.2.0 or higher:
sol10655: Change in Behavior: CR/LF characters appended to the HTTP monitor Send string
http://support.f5.com/kb/en-us/solutions/public/10000/600/sol10655.html
If you're already on 10.2.0 and you've captured a tcpdump of the failure, you could open a case with F5 Support to get help diagnosing the issue. Here is a link with some additional troubleshooting steps:
sol12531: Troubleshooting health monitors
http://support.f5.com/kb/en-us/solutions/public/12000/500/sol12531.html
Aaron