Error "Ambiguous name detected: My Function Name" after function has been used for months

[capson]

I am getting the error "Ambiguous name detected: My Function Name" this has happened a couple of times always I have been using the function since the project began this could be a year.

Then one day I open the workbook and I get the error message?

In this instance I get

"Ambiguous name detected: goFast" I use this everywhere in all my projects with never a problem, in this project for the last 7 months, I use it like so:

Sub MySub()
    
    goFast False
    
      Stuff

    goFast True
    
End Sub

If I comment out the goFast excel just finds the next instance and gives the same error

Any ideas what is going on here it is kinda freaking me out

Thanks

Sub goFast(Optional iReset As Boolean = False)

'Turn OFF various application properties
    Select Case iReset
        Case False
          With ThisWorkbook.Application
               .Calculation = xlCalculationManual
               .ScreenUpdating = False
               .DisplayAlerts = False
               .CutCopyMode = False
          End With
          
   'Turn ON various application properties
       Case True
         With ThisWorkbook.Application
              .Calculation = xlCalculationAutomatic
              .ActiveSheet.UsedRange
              .ScreenUpdating = True
              .DisplayAlerts = True
              .CutCopyMode = True
         End With
    End Select

End Sub