VB.net 3 Dropdown lists issue loading data from backend

[VBVZ]

Hi,

I have 3 dropdown lists. On changing the data in first control second controls data will be loaded from our backend(which is another application which takes request, params and will send us the result. depending on the selection of second control third controls data will be loaded in similar fashion. But here in the mean time after selecting the second control, before it loads the third control if i change first control data it is showing me a blank page. Please help...

thanks in advance
VBVZ