If you have an ERROR in the Yellowfin.log file that doesn't have a stacktrace at all:
YF:2015-02-10 12:47:38: INFO (MIDataSourceAction:execute) - MIDataSourceAction entered
YF:2015-02-10 12:47:38: WARN (MIViewProcess:loadViewSQL) - java.lang.Exception: SQL Document Id is NULL!
YF:2015-02-10 12:47:38:ERROR (MIViewProcess:loadViewSecurity) - Error: java.lang.NullPointerExceptio n
YF:2015-02-10 12:47:45: INFO (MIAdminAction:execute) - MIAdminAction entered
YF:2015-02-10 12:47:45: INFO (MIPreAdminConsoleAction:execute) - MIPreAdminConsoleAction entered
then sometimes the full stacktrace may be found in either the STDOUT log file (if the OS is Windows) or CATALINA.OUT (if the OS is Linux)