Alert Tones not Sync

Hi,

I purchased some alert tones through the iTunes store on my iPhone 4.

These tones have disappeared off my phone, and there is a little exclamation mark next to them on the iTunes ringtones screen for my phone.

I have found the files on my hard drive, and they play OK through iTunes.

How do I get these to sit back on my iPhone?

I purchased 3 alert tones on my iPad2, and they apppear on my iPhone. All of the alert tones that I bought on my iPhone also apper fine on my iPad.

I have tried all the solutions in other forum posts to rectify this, and a few others that I though of, but I cannot find anything that works.

Any help appreciated.

Thanks