Builds by default cache the externals in /scratch/condor-externals. If you're sharing the machine with others, you may collide and have problems. Solution, add
{code}
--DSCRATCH_STAGE:PATH=/path/to/a/private/directory
+-DEXTERNAL_STAGE:PATH=/path/to/a/private/directory
{endcode}
to your invocation of configure_uw
