Are the forms not linked like a parent/child? You should be able to just open the main form and have the child (subform) fill in automatically. Otherwise if they are not linked, an image could help see what you're trying to do.

Yes, they're linked. Here's the whole process: Via a search form (thank you Search Seminar), double click on a "Well" result and the WellDetail form opens, showing the Well details (whose Record Source is a query that includes LesseeID and LeaseID) and also showing the user the related Lessee and the related Lease. Lessees and Leases have a 1 to M relationship, as do Leases and Wells. From this WellDetail form the user can doubleclick on the Lease and another form opens with more detail - easy. But, when the user doubleclicks on the Lessee, I want a different form to open (the nested form) that shows the Lessee (in the main form) and opens to the Lease (subform) as was shown in the the WellDetail form, not just the first Lease in the subform, which are in numerical order. I'll attach 2 snips that I hope will clarify. I appreciate your help.

OK here we go......

First your Docmd.OpenForm is way outta whack (Well, Duh Scott, she just said it didn't work) because of incorrect concatenation.  I know, I know - bear with me.

The reason you get the type mismatch is because you are trying to put text into an id field.
If you just had:  DoCmd.OpenForm "MatterDetail_F2", , , "LesseeID=" & LesseeID
That would work.  
Now yours has:   DoCmd.OpenForm "MatterDetail_F2", , , "LesseeID=" & LesseeID AND ...
Access is trying to convert the where condition to  Lesseeid = LesseeID AND  instead of substituting the value of the variable - LesseeID = 9 for instance.  LesseeID AND is text and Access tries but says wait I can't do that. Text into a number field doesn't work.  So... type mismatch error.
Get it?

So to get that to work the proper concatenation you would have to do:
DoCmd.OpenForm "MatterDetail_F2", , , "LesseeID=" & LesseeID & " And LeaseID=" & LeaseID

Note the Space before the And   - " And

Regarding your forms.  While some what helpful - a capture of your form in design view is more helpful to us for seeing what is happening behind the scenes.

Lessee and lease are awful close.  Double check spelling.  I misread those at first.

If you click on the subform once and go to properties - make sure the relationship is correct between parent form and the subform.
See the example capture from the Blank template below.  

Concatenation... I tell ya... those quotes and ANDs will get ya.

Thanks for your help, Scott, I'll be working on it this afternoon.

Still not working. Here are the results of 2 (of many) different attempts-

Scott's fix:
DoCmd.OpenForm "MatterDetail_F2", , , "LesseeID=" & LesseeID & " And LeaseID=" & LeaseID
Generates an error message: Run-time error 3075  Syntax error (missing operator) in query expression LesseeID=84 And LeaseID=  I'm not sure how to express this, but is the code is not "finding" the LeaseID, because of the error?

My attempt:
DoCmd.OpenForm "MatterDetail_F2", , , "LesseeID=" & LesseeID & " And LeaseID=" & Lease_T_LeaseID
No error message, the MatterDetail form opens, but to blank records.

Are you working with a form and a subform here? If so, you will need to use the FULL name of whichever field is NOT on the same form as your code. For example:

Forms!LesseeF!LesseeID

and

Forms!LesseeF!LeaseSubformF.Form!LeaseID

See FormName.

Not working, yet.
DoCmd.OpenForm "MatterDetail_F2", , , "Forms!MatterDetail_F2!LesseeID=" & LesseeID & " And Forms!MatterDetail_F2!TestLease_SubF.Form!LeaseID=" & LeaseID
attaching error message

Yes, subforms are present in each form - but the LesseID and LeaseID on the form with the code, are located on the main form, not on a subform.

Since the end of the statement is saying it can't find LeaseID, check to make sure you spelled it right. The NAME property of the textbox that it's in has to be LeaseID, not just the control source.

Ah, right. The name property of the textbox and the control source are the same: Lease_T.LeaseID - made that change:

DoCmd.OpenForm "MatterDetail_F2", , , "Forms!MatterDetail_F2!LesseeID=" & LesseeID & " And Forms!MatterDetail_F2!TestLease_SubF.Form!LeaseID=" & Lease_T.LeaseID

But - Run-time error 424: Object required

You can't open a form like that with criteria from another different form. If Lessee is the parent form, you can ONLY open that guy up.

DoCmd.OpenForm "MatterDetail_F2", , , "Forms!MatterDetail_F2!LesseeID=" & LesseeID

Make sure that works first. Now, if you have a subform for the leases, and you want to show a specific one, you can change the RecordSource for the subform:

Forms!MatterDetail_F2!TestLease_SubF.Form.RecordSource = "SELECT * FROM Lease_T WHERE LeaseID=" & LeaseID

Try that.

The first code has definitely worked, but opens MatterDetail_F2 to the first Lease linked to that Lessee. I'd like the Lessee to open with the related Lease (in the subform) as shown in the requesting form.  
I'm sure I'm missing something (in addition to a some brain cells), as I don't understand how changing the RecordSource for the subform would work any differently than it does now, since they're linked correctly and working? Thanks, and I'll test more tomorrow.

You have to tell the subform WHICH lease to display. That's the LeaseID. That's why you're changing the recordsource for the subform. You're telling Access, "open this parent form, and then show this specific record in the subform."

You know what... someone else asked me a question very similar to this a few weeks ago. Let me dig it up and I'll use this example for my next TechHelp video. Hang in there.

Will do and thank you!

Here you go. Watch the Extended Cut: Open Form to a Specific Record

Awesome. I vote for Method One for it's flexibility to view other records and will try it! Thank you.

One and done. Very elegant solution.

You're very welcome. Sometimes it's just easier to SHOW you. :)