This directory should be moved to DRIVE:\usr\mibs, where DRIVE must be replaced with the driveletter where PHP is installed on, e.g.: c:\usr\mibs.
The Windows distribution contains support files for SNMP in the mibs directory. This directory should be moved to DRIVE:\usr\mibs, where DRIVE must be replaced with the driveletter where PHP is installed on, e.g.: c:\usr\mibs.