This is called during the delete process prior to the actual delete.
Edit Issue screen
public String ucEditPreDelete (
Problem pProblem, // the problem object
ArrayList pAttachments, // the list of attachments
ArrayList pInterestList, // the interest list
ArrayList pReleases, // the list of release
ArrayList pModules, // the list of modules
ArrayList pUdfs, // the list of udfs
SesameSession session, // current session
ProblemFormParam pfp) // values of from the form
It can return an error message to halt the process with an error condition, and its typical use is to prevent the deletion of an issue if a child issue exists.