Error: Unable to add a row: Object reference not set to an instance of an object

Scenario

You may get the following error message when opening
Time and Expense Entry
for the first time in a Practice CS session.
Error message
Unable to add a row: Object reference not set to an instance of an object
You can select
OK
and then proceed without further errors.

Cause

The error happens when the staff member's Time and Expense Entry
User Preferences
are set to default the
Sheet Date
to
Today's Date
, a default
Engagement
is selected, a default
Activity
is selected, and
Date
is set to default to
Sheet Date
.

Solution

Change one of the date default values or remove the
Engagement
or
Activity
default.