Problem in page Traverse when doing markups using leadtool...

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Hai all, i am using leadtool13 in my application ,and i am facing some problem in that,i have loaded five image in image viewer . i started to draw markups in first image ,without relesing left mouse button(without completing markups on that page) i am going into next page by pressing shotcut keys(like page down key) then my application is crasing. can anyone tell me where that problem would be. Anyone who used the leadtool can u please check this Scenario and let me know pls. how can i solve this crasing issue. thanks in advance. mahe