I need a good method to "lock" controls on a form, using a checkbox tied to a yes/no field in the record.

You need to add the other half:

If Me.chkLock = True Then
     Me.txtPlantcode.Locked = True
     Me.txtUsedFor.Locked = True
     Me.txtCostCenter.Locked = True
     Me.Abbrev.Locked = True
     Me.Project.Locked = True
     Me.txtWBS.Locked = True
     Me.txtTask.Locked = True
     Me.MaximoWO.Locked = True
     Me.ForBldg.Locked = True
     Me.Combo74.Locked = True
     Me.Combo82.Locked = True
     Me.Engineer.Locked = True
     Me.Planner.Locked = True
Else
     Me.txtPlantcode.Locked = False
     Me.txtUsedFor.Locked = False
     Me.txtCostCenter.Locked = False
     Me.Abbrev.Locked = False
     Me.Project.Locked = False
.....

But your seeming to say that you've already done that, so put a STOP right above the If check.  Trying adding a record.

You'll hit the stop.  use F8 to step through and see what's happening.

Jim.

I suspect the issue with this method is that the record doesn't exist yet when performing this check. Does that sound logical? When stepping through in creating a new record, it jumps straight to the else statement, skipping all of the locked = true lines. Is there perhaps a better method to lock up an entire form, without locking the subform tied to it?

The problem with your existing code on a new record -- besides not explicitly lining out all cases -- is our friend NULL
I am using a field in my underlying record which is a yes/no field, and a checkbox on the form tied to that field.
On a new record, that underlying field and checkbox will have a value of null, thus squirrelling up the logic

You my friend, are a genious. I really appreciate your excellent solution.

I think in this case though, allowing a null in the field is the error.  The initial state should be defaulted to false.

Jim.

I didn't write it up that way, but think about what you want to have happen if chkLock has a value of null.
Testing a control for null is always a pain, and likes to cause VBA to toss 'you have entered an expression that has no value' errors.
Someone will slag me for sure for saying it, but isnull() isn't my friend.  I never get bulletproof enough results from it to suit my tastes.

Now Nz() IS my friend, and while one is tempted to write
   Case Nz(Me.chkLock, True)= True 'existing record, chklock= null
        MyBoolean = True
You have to decide if that's the logic you want.

But Jim makes a good point.
Perhaps chkLocked should have a default value in the table.
That still won't fix things until a record gets created, but it takes null out of the equation after that.

I've run into another Expert who is ...extremely adamant... that null must never be permitted in boolean field, because you have to deal with its existence afterward.  And he dislikes how I describe the logic of how to deal with them.

Access is weird in that regard.  It permits null, but it has no way to display it.  Look in a Boolean field in a table with True, False and Null values -- you'll only see True and False.  The nulls are there.  Do a COUNT() on the field grouped by it and you'll get three results, one count of True, one count of False, and another count of False--which are the nulls.

Nulls happen and they have to be dealt with -- but if you can deal with them by not permitting them, that's easiest.

Another method to accomplish this is to use the Tag property of controls you want to be able to lock/unlock.  I put the value "Lock" in the tag property of those controls and then use code to loop through the forms control collection; something like, using Nick's code to set the value of MyBoolean

dim ctrl as control
for each ctrl in me.controls
    if instr(ctrl.tag, "Lock") then ctrl.Locked = MyBoolean
Next

Select allOpen in new window

It is easy to add the "Lock" value by selecting all of the controls you want to do this with at one time, and then typing the value "Lock" once, in the Tag property of all of those controls.

<<Access is weird in that regard.  It permits null, but it has no way to display it.>>

  Access does support a triple state check box.

Jim.

No disagreement there, I meant in the tables and in the query editor.  If you look in SQL Server Management Studio at a table with a bit field contain nulls, you see 1, 0, and NULL.  Link that table into Access and you see -1, and 0 and that's it.  You don't see null.