Hello Raj Dias,
your post isn't very helpful to help you. AFAIK the Free edition is no longer available for install, so this is perhaps Sophos Home (or maybe not).
An incompatible product is normally one of the other Sophos AV products. So - is it possible that sometime in the past a version of Sophos was installed on this Mac? If not, did you receive this pop-up on the very first attempt to install or perhaps later? I'd expect the log (if it exists) under /private/var/log/install.log.
Christian