[Simonadler]

I get a message "unsupported media format". How can I identify which songs are problematic and do I have to load them from I-tunes to my device individually?

[pacoman03]

What format are they, and how old are they? Older itunes songs were DRM protected.

[ChrisMay]

I get a message "unsupported media format". How can I identify which songs are problematic and do I have to load them from I-tunes to my device individually?

As PacoMan says, older iTunes files (they will probably have a file extension of .m4p) have copyprotection incorporated, and will only play on devices that are linked to the iTunes account they were purchased through, and PlayBook will not support this, and hence will not be able to play the files.
It may be possible to re-download them from iTunes without the copy-protection as iTunes no longer copy-protects its files (AFAIK)
I believe that there are ways of removing the copy-proptection, but they are probably illegal...

[wjptam]

Yes iTunes no longer DRM protects most audio files. The copy protected files are usually lower bit-rate than the DRM-free versions available now.

When the switch was made some years back, they offered to upgrade each protected song for the price difference. I don't think they offer that any more. Though if you pay to subscribe to iTunes Match, it should upgrade all your files to high bit rate DRM-free AAC files (even music in MP3 format you didn't buy from iTunes).