I downloaded Software_QTP_11.0_English_T6510_15066.iso file on my system from HP site to install QTP 11.
I have uninstalled QTP 10 from my system.Since this is an .iso file i am using a Daemon tool(from google) to mount the .iso file image and install QTP 11. However, i get an error message while installing QTP 11 "Setup has detected QTP or Quick test Add-in for QC, from ver 9.2 or earlier is installed on this computer.You must uninstall these before installing QTP 11".
I have checked again and again and i cannot find any traces of QTP 9.2 or QTP 10 on my system.
Apart from the above comment given by Rajkumar also go into registery using regedit through start RUN commnad and under software check for QTP Addin. If exists then delete directly from registry. Cheers.