Hi;
Windows 2000
IIS 5.0
Plesk 6.5 and horde webmail
Problem:IMP - webmail
--->>
Warning: Unknown(): open(C:\WINNT\Temp\sess_2a2e11ff8e1cee70ce559568dfee8d60, O_RDWR) failed: Permission denied (13) in Unknown on line 0

Warning: Unknown(): Failed to write session data (files). Please verify that the current setting of session.save_path is correct (C:\WINNT\Temp) in Unknown on line 0
<<---
Please help me..

It sounds like your web server does not have permissions to write to c:\winnt\temp. Either give it permissions, or let it write temporary files somehwere else. Also check your php.ini settings.