why would a boolean revert to an original value? - vba

Question

I know this might be a more of a general question, but I've looked at my code a 100 times and am not sure what's wrong. I set a global flag so that it can be used in different forms of my application.
Dim OverPopulated as Boolean
I have a function where I first set it to FALSE, and after it goes through some validating it gets set to TRUE.
Now i do a bunch of stuff, go through different forms, and the value stays correct the entire time. Basically I need this value for another form, so when I check
if OverPopulated = false then
MsgBox "You Can't do this and that"
exit sub
End if
Then all of the sudden it gets set to FALSE. I've went through every instance of OVERPOPULATED in my application and put a break point to it to make sure that nowhere do i set it to FALSE, except for the one time I set it to FALSE before my validation.
I only have it in 2 other forms in my applications. There is one place where the flag is being run twice through the same statement (just like the one above). The first time it goes through, the value is correct, then it goes through again and the value is set to FALSE.
Any ideas? if this is too vague, please let me know, I'll try to edit it.
EDIT: I deleted a lot of the code but here's how it looks.....
Dim OverPopulated as Boolean
' modular level
Private Sub ValidatePopulation()
Dim admDate as date
OverPopulated = False
admDate = Format(Now(), "mm/dd/yyyy")
Select Case revPURP
Case 0, 1, 2
'Check make sure these fields
'some if statements, checking, validation
Case Else ' no need to do a
End Select
OverPopulated = True 'I MAKE SURE IT GETS HERE and is set to TRUE!!!
End sub
Now, in other functions I used it like this...
If OverPopulated = False Then
If optStat (0).Value = True Or optStat (1).Value = True Then
MsgBox "You are not able to do this”, vbCritical, "Incorrect review status...."
TabPop.Tab = 6
End If
Exit sub
Else
'Proceed with SAVE
End If
So I have this. and I have another statement just like this somewhere else. This one gets hit twice. The first time I go through it line by line and it's FALSE, then the 2nd time around the value is TRUE.

Answer 1

It looks like for some reason the value was getting reset to FALSE. I took out the Dim OverPopulated as Boolean from my form code, and placed it in a GLOBAL module where all the other globals are stored. This seems to have fixed the issue of the value remaining the same while I'm manuevering in the application. Thank you for all your comments.
Global OverPopulated as Boolean