Have you created an Icon object?
Try passing Null for the Icon value - a default icon will be used.
Is
Markers.add a typo or bad copy/paste?
Markers.add(Marker1) is what's required.
Is
ovlMarkers a MarkersOverlay or a MarkersFocusOverlay?
Has it been initialzed?
Has it been added to the MapView?
Dim Markers As List
Markers.Initialize
For i=0 to 10
Dim Marker1 As Marker
Marker1.Initialize("Home sweet home", "bla", 52.75610, 0.39748, Icon)
Markers.add(Marker1)
Next
'add markers
ovlMarkers.AddMarkers(Markers)
Posting a ZIP'd project makes answering such a question so much easier.
Martin.