Horde Webmail not working on Linux server after Plesk upgrade

Have upgraded Plesk and now webmail access to mail is no longer working on the server via Horde. Need fixed ASAP!! psa-horde 3.1.7-rhel4.build84080425.19 Plesk Control Panel version psa v8.6.0_build86090814.11 os_CentOS 4.3 Operating system Linux [login to view URL] CPU AuthenticAMD, AMD Opteron(tm) Processor 6128 trying to log in via webmail in any of the accounts brings up the following error: The requested URL /horde/imp/[login to view URL] was not found on this server. Apache/2.0.52 (CentOS) Server at [login to view URL] Port 80