VBA - assign TextBox value to varaible error - vba

Question

I am writing a VBA code using a useform, which includes 3 ComboBoxes and 3 TextBoxes.
Whenever a user chooses any value from the list provided by the Comboboxes, the code works. The problems start when I try to combine a Combobox user's choice with any textbox.
I have assigned restrictions to the textboxes with a matching message box to pop up whenever the restriction is recognized, but when an appropriate value is typed into a textbox - I get a:
runtime error '91': Object variable or With block variable not set
While I don't have anything declared as an object or any "With" process throughout the entire code.
My code is:
Note: Num_Molecules is the combobox name, Molecules_Hand is the textbox name.
Private Sub Insert_Molecules_Click()
Dim lMolecules As Single
If Not Len(Trim(Num_Molecules.Value)) = 0 And Len(Trim(Molecules_Hand.Text)) = 0 Then
lMolecules = Val(Num_Molecules.Value)
ElseIf Len(Trim(Molecules_Hand.Text)) = 0 And Len(Trim(Num_Molecules.Value)) = 0 Then
Molecules_Hand.Text = ""
MsgBox "enter num of molecules"
'Exit Sub
ElseIf Molecules_Hand.Value < 5 And Len(Trim(Num_Molecules.Value)) = 0 Then
Molecules_Hand.Text = ""
MsgBox "value cannot be under 5"
'Exit Sub
ElseIf Molecules_Hand.Value >= 5 And Len(Trim(Num_Molecules.Value)) = 0 Then
If Not Val(Molecules_Hand.Value) = Int(Val(Molecules_Hand.Value)) Then
MsgBox "number must be an integer"
'Exit Sub
ElseIf IsNumeric(Molecules_Hand.Value) = False And Len(Trim(Num_Molecules.Value)) = 0 Then
MsgBox "textbox or choice cannot be empty"
'Exit Sub
End If
Else
lMolecules = Index_Form.Molecules_Hand.Value
End If
End Sub
The problem is with the last line before the "End If" - it just won't assign the textbox value to the variable. I have the same problem with all of my 3 textboxes and they are all assigned in the same way.
I'd appreciate your help.