Certain Songs dont sync to iPhone anymore

Hi,

I have a problem syncing my music from my Mac (OSX 10.8.2) via iTunes(11.0.1 (12)) to my iPhone 4S (iOS 6.01 (10A523)). I used to have an iTunes match prescription but let it expire recently.

It is impossible to sync certain songs to my iPhone. iTunes tells me that a whole Playlist has been synced but only halve of the songs are on my iPhone.

The songs play perfectly on iTunes and and are in different formats. It is also not possible to to sync them individually or in a new playlist.

They show up in "On this iPhone" view in iTunes, but the ones that dont show up on my iPhone are of a lighter color. They cant be played in this view, even htough they play without problems on iTunes. some of them are also duplicated even though i dont have two versions in my library.

Does anyone have an idea why this happens, its driving me crazy.

Thanks

Markus