I have the same problem as you sometimes! The form doesn't refresh properly.
Method 1
try this line of code instead of the current requery code. It shouldn't give you an error but may still not work due to bugs...
Form_frmSpendPlanSub.Requery
I use this format to reference across forms and it works well usually.
Method 2
1) What you can try is in design view click on the form that is doing the "After_Update"
2) Right-Click on the form and click "BUILD EVENT.." and select "Expression Builder"
In expression builder you can see exactly how the form you are in links to the form you want to get to and what you want to do...
So you would navigate yourself by going to FORMS--> Loaded Forms--> frmSpendPlanSub and then from the list you can double click on " " This will get you referenced to the form you want to affect. Then all you have to do is copy the code that it gives you in the box above into your VBA code and then reference what you want to do...
E.g.
Forms![frmMainForm]![frmSecondForm].Form![frmThirdForm].Form.Requery
Anyway hope that helps...