"DisplayPort Lower Setting Applied" - but seems to be ok.

Hi, i have just purchased a Samsung S23A750D (23", 120hz) monitor.

It's connected via DP to a Radeon HD5850. I also have an old Samsung 940B which is connected via DVI to the same card. Both monitors work fine, or it appears they do.
S23A750D: 1920x1080 (120hz)
940B: 1280x1024 (60hz)

I get an error when Windows first boots...

The system has detected a problem with the connection between your computer and the DisplayPort display that will prevent you from using the highest resolutions and/or refresh rates.

It gives me the option "Don't display this message again" and Clicking 'help' gives me this ('OK' just clears it):

Code:

Digital Flat-Panels (DisplayPort Monitors)

The My Digital Flat-Panels group becomes available in Standard View and Advanced View if you are using a digital display (such as a monitor or digital TV) that is connected through a DVI, DisplayPort, or HDMI™ connection.

A DisplayPort connection carries both digital and audio signal suitable for connecting to a home-theatre system. Use the various pages in the group to control how images appear on your display. Each page contains settings for configuring different display properties, such as improving image quality, performing color correction adjustments, and adding support for additional HDTV modes. 

For graphics cards that support the DisplayPort v1.2 standard, you can connect multiple DisplayPort displays to a single DisplayPort connection as long as the displays are compatible with the standard. Displays can be connected to a hub or using a daisy chain configuration. This type of multi-display capability is made possible through the multi-stream transport feature in the DisplayPort v1.2 standard. To determine the number of displays that can be connected to your card, see DisplayPort Diagnostic Information. For more information on the DisplayPort digital display interface and standard, see http://www.displayport.org.

 ?DisplayPort Connectivity?

If your digital flat-panel and graphics card are both equipped with DisplayPort connections, you can connect the panel to your computer using a single DisplayPort cable. This cable supplies video to your digital panel. To obtain audio, a separate connection must be made from the audio output of your computer to the audio input of your digital panel.
Note: You may first need to configure your digital panel for external audio. For more information see, the documentation for your panel.

It is also possible to connect a digital flat panel to a computer if the digital panel is equipped with an HDMI or DVI input. To do this, an HDMI or DVI cable and a DisplayPort-to-HDMI or DisplayPort-to-DVI adapter is required to obtain HDMI/DVI output from the DisplayPort connection on your graphics card. For HDMI, no additional connections are required for audio. For a list of AMD-recommended DisplayPort adapters and dongles, visit http://support.amd.com/us/eyefinity/Pages/eyefinity-dongles.aspx.

For anyone with ATI drivers, you may be able to replicate the info by going here:
file://localhost/C:/ProgramData/ATI/ACE/Help/en-US/cot1281990494122.html

I updated the drivers, but it still happens. Sometimes when flicking out of BF3 i get that message that asks if i want to take it to basic colours, but i don't think that's related (?).

The monitors both appear to be fine, their properties have the right resolution and refresh rate.

Any ideas?

Thanks :)

Oh, and after the first time i click 'ok' to rid the message, i immediately get another one:

The system has detected a link failure and cannot set the requested resolution and rfresh rate ond your DisplayPort display. Your display might not support the requested resolution or there may be an issue with the cable connecting the display to your computer.

It offers the same help.