Hallo VT610,
ich hab mal mit VB6 rumgespielt und kein Problem gefunden.
Hast du die Deklarationen den auch im Deklarationblock untergebracht?
Woander scheinen die nämlich nicht gültig zu sein.
Hier mal mein Beispiel:

Code:
Private Declare Function OpenDevice Lib "k8055d.dll" (ByVal CardAddress As Integer) As Integer
Private Declare Sub CloseDevice Lib "k8055d.dll" ()
Private Declare Function ReadAnalogChannel Lib "k8055d.dll" (ByVal Channel As Integer) As Integer
Private Declare Sub ReadAllAnalog Lib "k8055d.dll" (ByRef Data1 As Integer, ByRef Data2 As Integer)
Private Declare Sub OutputAnalogChannel Lib "k8055d.dll" (ByVal Channel As Integer, ByVal Data As Integer)
Private Declare Sub OutputAllAnalog Lib "k8055d.dll" (ByVal Data1 As Integer, ByVal Data2 As Integer)
Private Declare Sub ClearAnalogChannel Lib "k8055d.dll" (ByVal Channel As Integer)
Private Declare Sub SetAllAnalog Lib "k8055d.dll" ()
Private Declare Sub ClearAllAnalog Lib "k8055d.dll" ()
Private Declare Sub SetAnalogChannel Lib "k8055d.dll" (ByVal Channel As Integer)
Private Declare Sub WriteAllDigital Lib "k8055d.dll" (ByVal Data As Integer)
Private Declare Sub ClearDigitalChannel Lib "k8055d.dll" (ByVal Channel As Integer)
Private Declare Sub ClearAllDigital Lib "k8055d.dll" ()
Private Declare Sub SetDigitalChannel Lib "k8055d.dll" (ByVal Channel As Integer)
Private Declare Sub SetAllDigital Lib "k8055d.dll" ()
Private Declare Function ReadDigitalChannel Lib "k8055d.dll" (ByVal Channel As Integer) As Boolean
Private Declare Function ReadAllDigital Lib "k8055d.dll" () As Integer
Private Declare Function ReadCounter Lib "k8055d.dll" (ByVal CounterNr As Integer) As Integer
Private Declare Sub ResetCounter Lib "k8055d.dll" (ByVal CounterNr As Integer)
Private Declare Sub SetCounterDebounceTime Lib "k8055d.dll" (ByVal CounterNr As Integer, ByVal DebounceTime As Integer)

Private Sub Command1_Click()
WriteAllDigital (255)
End Sub

Private Sub Form_Load()
OpenDevice (0)
End Sub

Private Sub Form_Terminate()
a = CloseDevice()
End Sub
Gruß,
SIGINT

P.S.: Die Deklarationen hab ich direkt aus deinem Posting kopiert...