One of our customers has a point-to-point wireless connection, which started failing with an error that indicated problems with radio interference.  I ran the utility to check for busy radio channels, but it did not indicate any problems.  (Many channels came back as completely unused.)  I eventually reduced the transmit power of the root-bridge radio, which caused the connection to come back up. 

In retrospect, the issue was likely caused by a reflection that caused a second radio signal out of phase with the original signal.  This reduced or eliminated the signal at the antenna.