Loosing data in file upload inside a user control

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ASP.NET

user-controls

I'm using nested user controls in my aspx page. My page structure is as below.

Aspx > User Control 1 > User Control 2 > User Control 3

In User Control 3, I'm using a file upload control and an Upload button. When I try to upload file using Upload button, post back happening for the main aspx page and loosing the data in file upload.

Thanks in advance,
J