VBA just stops in Windows 7 but not Windows XP...

[TomCook]

**UPDATE**
This actuall does fail in XP as well, after a bit more testing. So confused.
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Hey folks,

So I've been scouring the internet since yesterday to try and figure out what the deal is with this, with no success. I have some code that, when run on my Windows XP machine in Excel 2010, executes flawlessly. On my Windows 7 (main) machine, however, when I get to any line that involves changing the Interior of a cell, the code executes that line, and then simply ceases. No error message, no nothing, the macro just stops running. At first I thought it was a problem with trying to tell a cell to be formatted in a way in which it was already formatted (I had had this issue with trying to tell a cell to have .NumberFormat = "$#,##0" when it already had that format), so I build in some if statements, which helped with the number formatting but now do not help on the following code:

Private Sub FillRangeInterior(r As Range, c As String, Optional comm As String)
    Dim pat
    Dim pci
    Dim col
    Dim tcol
    Dim tas
    Dim ptas
    Dim x

    Select Case UCase(Left(c, 1))
        Case "R":
            pat = xlSolid
            pci = xlAutomatic
            col = 255
            tas = 0
            ptas = 0
        Case "Y":
            pat = xlSolid
            pci = xlAutomatic
            col = 65535
            tas = 0
            ptas = 0
        Case "G":
            pat = xlSolid
            pci = xlAutomatic
            col = 5296274
            tas = 0
            ptas = 0
        Case "B":
            pat = xlSolid
            pci = xlAutomatic
            tcol = xlThemeColorAccent5
            tas = 0.599993896298105
            ptas = 0
        Case "1":
            pat = xlSolid
            pci = xlAutomatic
            tcol = xlThemeColorAccent5
            tas = 0.799981688894314
            ptas = 0
        Case "2":
            pat = xlSolid
            pci = xlAutomatic
            tcol = xlThemeColorAccent3
            tas = 0.799981688894314
            ptas = 0
        Case "3":
            pat = xlSolid
            pci = xlAutomatic
            tcol = xlThemeColorAccent4
            tas = 0.799981688894314
            ptas = 0
        Case Default:
            UnfillRangeInterior r
            GoTo DoneLabel
    End Select
    DoEvents
    On Error GoTo 0
    For Each x In r.Cells
        If x.Interior.Pattern <> pat Then x.Interior.Pattern = pat
        If x.Interior.PatternColorIndex <> pci Then x.Interior.PatternColorIndex = pci
        If x.Interior.Color <> col And col <> 0 Then x.Interior.Color = col
        If x.Interior.ThemeColor <> tcol And tcol <> 0 Then x.Interior.ThemeColor = tcol
        If x.Interior.TintAndShade <> tas Then x.Interior.TintAndShade = tas
        If x.Interior.PatternTintAndShade <> ptas Then x.Interior.PatternTintAndShade = ptas
    Next x
DoneLabel:
    If comm <> "" Then r.AddComment comm
End Sub

It's ugly, I know. It was a lot cleaner when I had first written it; this is the result of me trying various means of solving the issue, but to no end. Any place in that code when I try to assign a value to x.Interior.<something>, the code will do so, and then just stop. Other than simply finishing this project on my XP machine (which isn't really a viable long-term solution as we're eventually all moving to Windows 7), can anyone offer some insight or suggestions as to what is going on and how to fix it?

Thanks,
Tom