i encountered the same thing when creating a user control which has esri's controls inside. while "breaking my head" to figure out what can possibly go wrong i figured out it has something to do with their new license initialization workflow: 1. put in each user control ,at the 1st line of its deafult constructor, the esri.arcgis.bindinglicense.bind( ..) line. 2. rebuild your project. this worked out for me. you can also ask the "designmode" flag because it is redundant in runtime. moreover i converted my project from 9.3.1 to 10.1 and i encountered a strange behaviour and hard application crashes (it skips try..catch and application exits). it appears that my old checklicense() function was written a little bit different than current up to date esri's license check sample. i was checking for product code availability and just then i initialized license- everything seem to work but on several points when accesing esri's objects the app closed immidietly. again my blames were focused on license- on last esri's documentation they call aoinitialize.init() and just then they check for product availability.. clearly they have a bug but again my application is stable now.. hope it will help you..
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