fix a bug in an error message in compute that I noticed in production logs
fix a bug in an error message in compute that I noticed in production logs

tscholl2/smc,sagemathinc/smc,tscholl2/smc,tscholl2/smc,tscholl2/smc,sagemathinc/smc,DrXyzzy/smc,DrXyzzy/smc,DrXyzzy/smc,sagemathinc/smc,tscholl2/smc,sagemathinc/smc,DrXyzzy/smc