on this iphone section of itunes, music unavailable and unerasable

Hello,

I'm using last version og itunes with my iphone 4 ios 7.1 and since a long time i have several music unvailable in the section on this iphone in itunes.

I'm not able to erase the music has it's appears in grey as in the picture below:

does anyone encounter this issue?

I don't know how to resolve this.

restore of iphone, don't solve this issue.

thnaks in advance for your help.

Regards