Explanation:

If you see "SQL error: User-defined exception signaled" displayed instead of the Foxhound page you expect, try using the Foxhound Options - Diagnostics - Display Diagnostics button to see if there are any diagnostic messages associated with this problem.

You may see one or more messages like this:

342 2012-11-14 17:21:26.237 Full Build 4215a 1559 210a-a7(210eh1) SQLCODE = -297, SQLSTATE = 99010, ERRORMSG() = Internal error 99010
343 2012-11-14 17:21:26.238 Full Build 4215a 1559 210a-d1b(210eh1) SQLCODE = -297, SQLSTATE = 99010, ERRORMSG() = Internal error 99010

The following "Internal error" values may indicate that the Monitor Options settings have been deleted or become corrupted for a sampling session. In this case the workaround is to stop sampling, delete the affected sampling session, and then restart sampling for that target database.

99001 99002 99003 99004 99005 99006 99007 99008 99009 99010 
99011 99012 99013 99014 99015 99016 99017 99018 99019 99020 
99021 99022 99023 99024 99025 99026 99027 99028 99029 99030 
99031 99032 99033 99034 99035 99036 99037 99038 99039 99040 
99041 99042 99043 99044 99045 99046 99047 99048 99049 99050 
99051 99052 99053 99054 99055 99056 99057 99058 99059 99060 
99061 99062 99063 99064 99065 99066 99067 99068 99069 99070 
99071

In particular, the message "Internal error 99064" may indicate that the sampling session currently displayed on the Monitor Options page has been deleted, perhaps when the Delete Multiple Monitor Sessions. In that case, Foxhound mistakenly tries (and fails) to display the deleted set of Monitor Options instead of switching to the "Default Settings". The default workaround is to close the failing Monitor Options page, and open it again for a different sampling session, or for the "Default Settings" which is never deleted.

Please report this error; see How do I report unexpected errors and exceptions?

See also...
How do I see Foxhound diagnostics, errors and exceptions?
How do I run adhoc queries on the Foxhound database?