Run Time Error 9 Subscript Out of Range - Happening to only 1 user?

Hi Guys,

I am stumped with this error, which seems to be happening to only one of my users...

I have a long code, which starts with declarations including a sheet name. The sheet name is the current month in the form MMM-YY, e.g. 'Feb-15'. This is to select the worksheet in another workbook with that sheet name later on in the code.

Option Explicit
Sub SaveButton_Click()

Application.ScreenUpdating = False
Application.Calculate

Sheets("Copy").Range("CG1").Value = "some text goes here"

PleaseWait.Show vbModeless
DoEvents

    Sheets("Copy").Select
    Sheets("Copy").Range("D2:D9").Value = Sheets("ONE").Box1.Value
    Sheets("Copy").Range("E2:E9").Value = Sheets("TWO").Box2.Value
    Sheets("Copy").Range("A11:U18").Value = Sheets("Copy").Range("A2:U9").Value

    Dim FName As String
    Dim IsClosed  As Boolean
    Dim strSheet As String
    Dim strTeam As String

strSheet = Workbooks("Book1").Sheets("Copy").Range("D20")
strTeam = Workbooks("Book1").Sheets("actions").Range("U54")
FName = "//the file path goes here/" & strTeam & " - Log.xlsm"

'More Code Goes Here......

End Sub

The code that is highlighted when the user gets the run time error is the "strSheet =" line.

"Book1" is the ActiveWorkbook where the code runs. "D20" has the formula "=TEXT(TODAY(),"MMM-YY")" and currently shows Feb-15 which is a valid sheet within the workbook that will open later (FName), (although when the code crashes, it is only setting the string name).

However, this code all runs fine for me, it's just happening to one user. Also, it was working all throughout January for him (when D20 showed Jan-15), only now in February it has stopped working, so maybe it is the Feb-15 bit??

Does anyone have any ideas on why it would crash on that line??

I was thinking maybe it is the user's own Excel settings?

Thanks,
ExcelNat

No not really, I've already checked that he's using the correct version of Book1 too. Book1 is saved on a network drive as ReadOnly and all users (about 24 users) access the same Book1 which they enter data into and it then goes and saves onto the relevant spreadsheet (FName). And as I said, all other users are doing fine. When I replicated what the problem user had just done, I got no errors at all.
I think this is probably more of a computer issue. Maybe a reboot will do the trick?!

Changed it to ActiveWorkbook instead and that seems to have worked!!!

Still baffled as to why it even did it in the first place!

Thanks for your help :-D