im sorry,

 

this issue occurs if you dynamically change Thread.Culture via

 

Protected Overrides Sub InitializeCulture()

 

this (ofcourse) only changes the cuture for the page.handler (aspx) and not for those you implemented to draw up the contextmenus.

 

after moving the  programatic culture change from "InitialiseCulture" to "Application_PreRequestHandlerExecute" everything works fine.

 

maybe this helps someone else...