This usually means that tempo isn't happy with its input.
Run dspsr in very verbose mode (with the -V command line option), redirect stderr to a file (with >& in C shell; with 2> in Bourne shell) and search for the system call to tempo. (The relevant line should have the characters -z in it.) This will show you how dspsr is running tempo. You can then
and run this command to see what tempo thinks about it.