should
DataEntryForm.Controls(ComboBox1).SetFocus
read
DataEntryForm.Controls("ComboBox1").SetFocus
?

DataEntryForm.Controls(combobox1).SetFocus

is wrong. The Controls index  should be a string naming the control, or an
integer index into the controls collection. But why not simply do

combobox1.SetFocus

Please also change  your

If combobox1 = "1" Then

to

If combobox1.Value = "1" Then

(If nothing else, this will remind you that you are dealing with an object
that has attributes and methods available.)

The event handler almost certainly got into trouble at the
Controls(combobox1) call. It possibly took the value from the combo box (a
string "1"), converted it to an integer, and set the focus to the first
control. Or it might just have crashed looking for a control called "1".

However, there is also the fact that you are doing this from a text box exit
event, and the move  that caused the exit might happen after the exit event
completes. You might need to set the event's "Cancel" parameter to true to
get it not to do the move. Try without it first, but put it in if you're
still having trouble.

BTW, you don't need Exit Sub in your If statement. Without it, execution
will reach the Else, then jump past the End If and reach the End Sub - which
is what you want to achieve.

you are correct about the missing quotes... Unfortunately, that was
just an editing error on my part when I tried to simplify the posted code.
Actual code  does have the control name quoted, but is still is causing problems.

Thanks for taking the time to offer such a detailed response and set of
suggestion. Also accept my apologies for this delayed response to your reply.

My error with the control index  (also pointed out by Pascal), was actually an
editing error on my part when I tried to simplify the post. My actual code  was:
DataEntryForm.Controls("cbT_Code1").SetFocus

You also offered the comment :
".However, there is also the fact that you are doing this from a text box
exit event, and the move  that caused the exit might happen after the exit event
completes."

This proved to be the thing I need to resolve my problem. With a clear head the
next morning, I discovered (through careful observation as I manually stepped
through the code) that your comment was right on the mark. The problem proved
to be with using the <Tab> key when moving through the cells... Even though
SetFocus was been executed, the Exit Event insisted on issuing the <Tab>.

Because of some "Enter Event" code associated with combobox1 (or further
ignorance on my part), I had no success with "Cancel = True" in the textbox1
Exit Event. The code executed the line without error, but the <Tab> still
occurred.

I finally ended up moving the conditional test to the textbox1 Enter Event and
added a Boolean flag that is tested/trapped in the combobox1 Enter Event. This
finally resolved my problem.