Can't play music on iPhone

[firehousemouse]

I have an iPhone 4, and after updating it to iOS 5 most of the music on the iPhone is unavailable. It is all viable but most is a washed out grey & won't play. I have tried restarting the iPhone. Taking the songs off & putting them back on, it takes the full time to put them back on & says it is taking up memory but I still can't play them. There are only a couple songs that I can play and they are the normal black, not the washed out grey. any ideas?
Thanks

 

[macthak]

I also have the same problem. Please help

 

[verwon]

Completely unsync and resync a few times, or restore your phone.

 

[BlackTofu]

Most of time I will delete all of music of my iPhone and then sync again.