Returns string error message.
This function returns the string error message
explaining the error generated by the last LDAP command for
the given link_identifier
While LDAP errno numbers are standardized, different
libraries return different or even localized textual error
messages. Never check for a specific error message text, but
always use an error number to check.
Unless you lower your warning level in your php.ini sufficiently or prefix your LDAP
commands with @ (at) characters to
suppress warning output, the errors generated will also show
up in your HTML output.
See also ldap_err2str() and
ldap_errno().