File Upload Control strange behavior

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ASP.NET

HI,

I am having a strange issue with my code,

I have an asp File Upload Control in my application. and I have a function against it which is taking the file from it and saving it in a temp directory of the project.

Now when user again uploads a file, it replaces the old file with newly uploaded one.
That is fine, and actually what I want,

But I am trying same code on another machine, and there rather replacing the old file, it is creating a separate new file, even with the same name and new content.

For Example, if i uploaded a file "ABC" in temp directory, on 2nd upload, it is placing ABC again in that directory so that 2 ABC files are there,

while it should either save it like ABC(1) etc. as Google Chrome does, with duplicate files,

Any Idea's??