[otrs] SysConfig Error

Hi, when using OTRS 2.0.4 on RedHat (with Postgres 7.4.8 backend), I have been experiencing a problem with OTRS' SysConfig. When I want to update eg. "Config Options: Ticket -> Frontend::Agent", I get the error message "Message: Can't write ConfigItem!", which appears on line 130 of Kernel::Modules::AdminSysConfig::Run. In error log I can find also a "Message: Need Value!" error message, which is caused on line 360 of Kernel::System::Config::ConfigItemUpdate. Because I cannot find any satisfactory answer on google, I want to ask you, if anyone of you met error like this and what should be the reason of it? Thanks in advance, David