This issue seems to be isolated, and appears to occur only in an older version of our software (with an "older" version of the task scheduler source code). It doesn't occur in newer versions of our software.
The TaskEditDialog with the General tab active is shown with the following settings:
o Trigger is based on time schedule (specific date and time), ran once only.
o Run whether user is logged on or not is checked.
o Do not store password is checked.
o All other settings are default settings.
I'll take a look at some validation code for the "Run with highest privileges" option when the OK button in the TaskEditDialog is clicked.