FindText function doesn't work in Acrobat XI

I have a simple code compiled with the new Acrobat.tlb file, where I show a Pdf file in my application.

My .exe file works correctly on the PC with Acrobat Pro 9 installed.

In the pc with Acrobat X and Acrobat XI the FindText function doesn't work. The function return -1 (success) but the text isn't selected and the page isn't scrolled over the text.

Please can you tell me how I can approach?

If you want I can attach the code.

My customers will buy Acrobat Professional if this function works, it is better for us and for you if you help me in order to solve this drawback.

I hope in a fast answer.

Domenico Pirilli