The [3828.1968][-conn:openacs::0] identifies a process associated with a page request. If lines just above this error message include identical references, then they are part of the same process. You might find that there is more useful information just above the error message you posted. The information might include the location of the file making where the error originates from etc.

The error is stating that the procedure does not exist.

The api-doc at http://openacs.org/api-doc/proc-view?proc=auth%3a%3aself%5fregistration

states that it is located at: {serverroot}/packages/acs-authentication/tcl/authentication-procs.tcl

Is the procedure there in the system that has the error?

If so, you might check the package manager at your site's /acs-admin/apm/ to verify that all the code has been loaded, if you recently upgraded. Then restart the computer (or at least aolserver).

You might also see if this is the result of an existing bug, such as this:
http://openacs.org/bugtracker/openacs/bug?bug_number=1637