I have an add-in which works well on my machine.
Running it on another machine I get a compile error with the Mid function
highlighted. Are thee a simple explanation for this?

Sub GetSTGfilesFromProjectFile()
Dim firstLine As Boolean, firstSmp As Boolean, firstPlot As Boolean
Dim fileFilter As String, Title As String, fullFileName As String, file As
String, root As String
Dim saveStatusbar As String, stgFile As String, sheetName As String, errMsg
As String
Dim pos As Integer, fileNumber As Integer, oldSheetsInNewWorkbook As
Integer, i As Integer, posSlash As Integer, posDot As Integer
Dim data, radialP(), words(), stgFiles(), shearingFiles(),
consolidationFiles(), projectInfo(), poreWater()
Dim wb As Workbook
Dim ws As Worksheet
Dim rng As Range, rng2 As Range

fileFilter = "stg files (*.prj),*.prj," & "All files (*.*),*.*"

Title = cGeoData & " Select Project File to Import From..."
fullFileName = Application.GetOpenFilename _
(fileFilter:=fileFilter, _
FilterIndex:=1, _
Title:=Title, _
MultiSelect:=False)
If fullFileName = "" Or fullFileName = "False" Then Exit Sub
pos = InStrRev(fullFileName, "\")
root = Mid(fullFileName, 1, pos)

fileNumber = FreeFile 'FreeFile function