could you elaborate on the issue more ?
need to execute the RFT script on a click of a button
which button are you referring to ?
EDIT - I hope it's not too late , What I understand is that from your application (ASP.NET based) , you want to execute an RFT script based on the parameters of the input fields in the application .
For that depending on the type of RFT scripts you have (VB scripts or Java Scripts)
you can use one of the following:
java -jar <BIN>\rational_ft.jar -datastore <path to the project> -playback <scriptname without extn>
or
<BIN>\rational_ft.exe -datastore <path to the project> -playback <scriptname without extn>
Both , rational_ft.jar and rational_ft.exe reside in the BIN directory of RFT installation .
(Usually C:\Program Files\IBM\SDP\FunctionalTester\Bin on a 32 bit windows machine).
From your application you would need to be able to start a process and you should be good to go.