http://www.linuxprinting.org/error_log-faq.html

Section 1: General Questions

1.1 In which forum should I ask CUPS related questions?
1.2 What is the error log?
1.3 What is the name of the CUPS error log?
1.4 Where is the error_log?

Section 2: Enabling Logging

2.0 See also the Enabling Logging database page.
2.1 How come the error_log doesn't show much information?
2.2 How do I change the logging level?
2.3 After enabling Logging, why are no more error reported to the error_log file?

Section 3: CUPS Log Errors

3.0 See also the CUPS Log Errors database page.
3.1 Why are there no references to ghostscript in the log?
3.2 cupsd: Child exited with status 1!
3.3 unable to evaluate datablob
3.4 cupsdoprint: relocation error: cupsdoprint: undefined symbol: strlcpy
3.5 Warning - hp_psc_950: Bad printcap entry - missing 'sd' or 'client'
3.6 /usr/local/sbin/lpdomatic: unable to evaluate datablob
3.7 media tray empty
3.8 [Job 28] /usr/lib/cups/filter/foomatic-rip: No such file or directory
3.9 "/usr/local/var/spool/cups/d00032-001" - Permission denied
3.10 Denying user "" access to printer?
3.11 /usr/bin/foo2zjs-wrapper: line 141: gs: command not found?
3.12 Unable to convert file 0 to printable format for job 4!
3.13 Couldn't exec foomatic-gswrapper -q?
3.14 Error: /invalidfont in findfont?
3.15 YOU DO NOT HAVE YOUR FONTS INSTALLED!!?
3.16 server-error-service-unavailable?
3.17 sh: line 1: hpijs: command not found
3.18 Can't find initialization file gs_init.ps?
3.19 Unknown device: ijs?
3.20 cat: write error: Broken pipe?