Error if logfile is already open

I use this code to test if I have a text file open. If it is already open it should either close it and reopen it or just associate it with #f. I have tested numerous ways and I cannot get it to work:

[VBA]Function IsFileOK(stgFullPath As String, stgFileName As String) As Boolean

Dim f As Integer
IsFileOK = True

On Error GoTo FileProblem
f = FreeFile
Open stgFullPath For Append As #f

Exit Function

FileProblem:
Close stgFileName
Open stgFullPath For Append As #f
'IsFileOK = False

End Function
[/VBA]

P.S. I use this textfile as a logfile to log what my users do with my program.

[vba]

Function IsFileOK(stgFullPath As String, stgFileName As String) As Boolean

Dim f As Integer
IsFileOK = True

On Error GoTo FileProblem
f = FreeFile
Open stgFullPath & stgFileName For Append As #f

Exit Function

FileProblem:
f = f - 1
Close #f
Open stgFullPath & stgFileName For Append As #f
'IsFileOK = False

End Function
[/vba]