Program stops working on 2nd runthrough - vba

Question

Visual Basic Problem:
Hello Friends,
my problem is pretty complex (although the solution is most likely an easy one):
I've written a small application in Visual Basic. It's a small time management system that has 4 simple functions (on separate buttons):
"Start Work:"
Fetch the current date from System, compare it to a list of dates in an excel table, set current row to the row with the fitting date, and enter the current time in the appropriate cell.
The other functions are "stop work", "start break" and "stop break" and work pretty much the same way.
The application is started by a button embedded in the form and works - so far so good. If I however, start VBA's own debugger and then start the Program again, it fails, because the function that sniffs the correct date out of the list of dates fails to find the correct value. At this point I'm pretty much out of ideas (especially since this is my first VBA project) so I'd be really glad if someone could give me a pointer in the right direction.
Here's the function fetching the date:
Function get_date(time As Date) 'findet das aktuelle Datum in Spalte 2 (Datum)
Dim findDate As Range
On Error Resume Next
Set findDate = Columns(2).Find(Date)
Err.Clear
On Error GoTo 0
If findDate Is Nothing Then
MsgBox "Current Date not on Active Form!"
Else: MsgBox "Current Date is " & Date
MsgBox findDate
Exit Function
End If
End Function
and the function setting the row to the row with the current date
Function get_row(time As Date)
Dim rngSearch As Range, rngFound As Range
Set rngSearch = Range("B5:B18")
Set rngFound = rngSearch.Find(What:=Date, LookIn:=xlValues, LookAt:=xlPart)
If rngFound Is Nothing Then
MsgBox "Aktuelles Datum nicht gefunden - Terminplan erweitern"
Else
get_row = rngFound.row
End If
End Function
As I mentioned both those functionalities work perfectly fine on the first start-up of the form but fail to find (and thus return) a value if I debug and start the Makro again.
The program also has a real time running clock on a timer - maybe that's a factor? I'm totally lost to be honest.
Any criticisms towards the code and how I tackled certain problems are also very welcome - this is my first VBA app ever.
Update:
As requested here's a screenshot of what I assume to be the search ranges:
I'm using the 1904 date system, but changing back to 1900 didn't have any effect.
If anyone is interested, I uploaded the whole Project into my github Stechuhr.xlsm
The relevant file is "Stechuhr.xlsm"
Any further help will be greatly appreciated.
Edit: To clarify - The program stops working, once it has been paused and then resumed. I suspect that the timer function is somehow responsible for this - will do further testing.
Update 2:
As I have been unable to fix this, I simplified my problem as suggested:
Option Explicit
Public Function FindDateRowInColB(TargetDate As Date, TargetSheet As Worksheet) As Long
Dim FoundRange As Range
Set FoundRange = TargetSheet.Columns(2).Find(What:=TargetDate, LookIn:=xlValues, LookAt:=xlPart)
If FoundRange Is Nothing Then
FindDateRowInColB = 0
Else
FindDateRowInColB = FoundRange.Row
End If
End Function
'Test Button 1
Private Sub Test_button_Click()
Dim TestTime As Date
Dim TestSheet As Worksheet
Dim TestRow As Long
Dim pdat_Datum As Date
pdat_Datum = Date
'set references
Set TestSheet = ThisWorkbook.Worksheets("Tabelle1")
'this is our test assertion
TestRow = FindDateRowInColB(pdat_Datum, TestSheet)
'short if statement to display a message based on test results
MsgBox ("TestRow =" & TestRow)
End Sub
' Test Button 2
Private Sub TestButton_2_Click()
Dim active_row As Integer
Dim pdat_aktuellesDatum As Date
Dim TestSheet As Worksheet
pdat_aktuellesDatum = Date
Set TestSheet = ThisWorkbook.Worksheets("Tabelle1")
'set references
Set TestSheet = ThisWorkbook.Worksheets("Tabelle1")
active_row = FindDateRowInColB(pdat_aktuellesDatum, TestSheet)
MsgBox ("Die passende Reihe zum heutigen Datum ist " & active_row)
End Sub
There's the code. It's simply one function and 2 buttons to test it. However, it has the very same problems as my original code - works fine on first startup, but if I ever pause the program and start it again, FindDateRowInColB always returns a value of null. I suppose there might be some memory management issue at work.
If anyone has further input, it will be greatly appreciated.

Answer 1

You could create a lightweight test environment for your functions to make sure they are returning what you'd expect for a few conditions. Here is an example function for finding a date match in column B along with two tests:
Option Explicit
Public Function FindDateRowInColB(TargetDate As Date, TargetSheet As Worksheet) As Long
Dim FoundRange As Range
Set FoundRange = TargetSheet.Columns(2).Find(What:=TargetDate, LookIn:=xlValues, LookAt:=xlPart)
If FoundRange Is Nothing Then
FindDateRowInColB = 0
Else
FindDateRowInColB = FoundRange.Row
End If
End Function
Sub TestFindDateRowFunctionSuccess()
Dim TestTime As Date
Dim TestSheet As Worksheet
Dim TestRow As Long
'set references
Set TestSheet = ThisWorkbook.Worksheets("Sheet1")
TestTime = "4/22/2014"
'this is our test assertion
TestRow = FindDateRowInColB(TestTime, TestSheet)
'short if statement to display a message based on test results
If TestRow = 3 Then
MsgBox ("Test passed! Identified 4/22/2014 in row 3")
Else
MsgBox ("Test failed! Did not identify 4/22/2014 in row 3")
End If
End Sub
Sub TestFindDateRowFunctionFailure()
Dim TestTime As Date
Dim TestSheet As Worksheet
Dim TestRow As Long
'set references
Set TestSheet = ThisWorkbook.Worksheets("Sheet1")
TestTime = "4/1/2014"
'this is our test assertion
TestRow = FindDateRowInColB(TestTime, TestSheet)
'short if statement to display a message based on test results
If TestRow = 0 Then
MsgBox ("Test passed! Date 4/1/2014 was not found so 0 was returned")
Else
MsgBox ("Test failed! Date 4/1/2014 was identified somewhere")
End If
End Sub