[Koha] Can't enable Plugins

[Sami M. Rasheed]

Hi  Bob Ewart
I apply all steps for koha plugins, I had the following error:
Software error:
Undefined subroutine &main::/var/lib/koha/koha/plugins called at (eval 60) line 2.
	...propagated at /usr/share/perl/5.18/base.pm line 83.
BEGIN failed--compilation aborted at /usr/share/perl5/Authen/CAS/Client/Response.pm line 68.
Compilation failed in require at /usr/share/perl5/Authen/CAS/Client.pm line 8.
BEGIN failed--compilation aborted at /usr/share/perl5/Authen/CAS/Client.pm line 8.
Compilation failed in require at /usr/share/koha/lib/C4/Auth_with_cas.pm line 25.
BEGIN failed--compilation aborted at /usr/share/koha/lib/C4/Auth_with_cas.pm line 25.
Compilation failed in require at /usr/share/koha/lib/C4/Auth.pm line 59.
BEGIN failed--compilation aborted at /usr/share/koha/lib/C4/Auth.pm line 68.
Compilation failed in require at /usr/share/koha/intranet/cgi-bin/plugins/plugins-home.pl line 26.
BEGIN failed--compilation aborted at /usr/share/koha/intranet/cgi-bin/plugins/plugins-home.pl line 26.

Sami Al-Asheh