Construct a xls file name and open/activate it

[grntrnr]

I am not able to construct a workbook file name as a string and use it to activate a workbook.

Option Private Module
Public wbVersion As String
Public sFilePath As String
Public wbCntl As Workbook
Public wbFilename as String

Sub SetConstantVariables()
wbVersion = " v12.xls"
sFilePath = "I:\Documents and Settings\Grant\My Documents\NeuroFission\Development\"
wbFilename = sFilePath + "Control" + wbVersion
wbFilename.Activate
or
Workbooks(wbFilename).Activate
etc
.
.

Apparently, none of the methods for activating the workbook works for me, using a predefined string name for the workbook. Can this be done? What might I be doing wrong?
Grant

[kadghar]

perhaps if you open it first:

Workbooks.open(wbfilename)

then activate it.