The server has not been set to compile php with pear. You need to recompile it. You can test if pear is available on your server by running 'which pear'. If it is available it will show the pear path.
 
[root@server ~]# which pear
/usr/bin/pear
 
If not, it will show nothing or display the error.
 
For cPanel server:
Please go to root WHM -> Software -> EasyApache (Apache Update). And recompile your apache+php, make sure Pear is enabled while configuring PHP options.