VirtualWire / Mega 2560

Code that worked fine on a Mini Pro is not working on a Mega. I'm sending data via RF with VirtualWire, and only the first send is "getting through".

This conditional does not appear to be met with any subsequent sends:

if (vw_get_message(buf, &buflen))

This one has me baffled. Timer issues?

Any ideas on this? I've Googled my fool head off. My code is straight out of the book, so to speak. No problems with the 328.