The seven crew, including Japanese astronaut Soichi Noguchi, were already aboard the orbiter when NASA managers postponed the flight just two hours and 20 minutes before scheduled liftoff.

From Amsat Sarex reflector:
NASA has scrubbed the launch (July 13) of Discovery because of a problemwith a fuel tank sensor designed to protect the Shuttle's engines byshutting them down if fuel runs low.
Kenneth - N5VHO

Just FYI - here's a low technology method that has worked the last few days to connect to the ISS for PMS and digipeating. I have an ICOM 229H connected to an old KPC-3 with a magnet mount antenna placed on a metal roof angled north. I use the windows terminal emulator HyperTerminal for software. I wasn't expecting this to work but it does the job very well.

Rich Lovin, N7VIY