Resolved! Thank you, you are a genius!! I have created a new signed certificate and assigned that in server --> Restarted the server--> Restored the iOS on the iPad. Then tried the enrollment it worked.
Still I am receiving some errors(below) in Service_proxy_error.log. Is that normal?
[Thu Oct 25 13:52:53.350885 2018] [ssl:info] [pid 18309] (54)Connection reset by peer: [client 10.100.55.69:52056] AH01991: SSL input filter read failed.
[Thu Oct 25 13:52:53.350916 2018] [ssl:info] [pid 18338] (54)Connection reset by peer: [client 10.100.55.69:52054] AH01991: SSL input filter read failed.
[Thu Oct 25 13:52:53.350910 2018] [ssl:info] [pid 18308] (54)Connection reset by peer: [client 10.100.55.69:52057] AH01991: SSL input filter read failed.
[Thu Oct 25 13:52:53.350907 2018] [ssl:info] [pid 18311] (54)Connection reset by peer: [client 10.100.55.69:52055] AH01991: SSL input filter read failed.
[Thu Oct 25 13:52:53.351107 2018] [ssl:info] [pid 18335] (54)Connection reset by peer: [client 10.100.55.69:52053] AH01991: SSL input filter read failed.
[Thu Oct 25 13:52:53.351322 2018] [ssl:info] [pid 18315] (54)Connection reset by peer: [client 10.100.55.69:52060] AH01991: SSL input filter read failed.
[Thu Oct 25 13:53:42.923648 2018] [ssl:info] [pid 18272] (54)Connection reset by peer: [client 10.100.5.85:64996] AH01991: SSL input filter read failed.