Error 91: Find Locating Text On Another Worksheet

I have a single button on a spreadsheet. When clicked, it gives me Error 91: Object Variable or With Block Variable Not Set. This is the button's


Private Sub Analyze_Click()
Dim TextToLocate As String
Dim Searching As String
Dim TechNum As String

TextToLocate = "Mobile Device : "

Fname = Application. GetOpenFilename("@Road Excel Files,*.xls", , "Open @Road Log File")
Workbooks.Open (Fname)

' Error here at cells.find:
Searching = Cells.Find(What:=TextToLocate)
TechNum = Replace(Searching, TextToLocate, "")
TechNum = Left(TechNum, 5)
MsgBox TechNum

End Sub

The purpose of the code is to:Allow the user to open a log fileIn the newly opened log file, find the string "Mobile Device : "Following "Mobile Device : " is a tech number. Strip out "Mobile Device : " and grab the first 5 characters of the tech number.Show me what the tech number is in a message box
If I insert the code into the actual log file (no button and no opening of files), it works fine. I searched this forum and others and used everything I learned to find a solution, but the error remains.