1) can we install it on forwarders (which is forwarding logs and it is a HEAVY FORWARDER)??
I never tried to install it on a heavy forwarder, only on search head, but I believe you can install on HF and send the data to an specific index/sourcetype to index the data and try to run the reports from search heads.
2) as i installed the above mentioned (question) error pops up??
please visit the link below and run the solution provided there. I ran it and it had fixed my problem, as it is the same as you have.