Error in Sync iPhone 4 or 4S iOS5 with iTunes

Hello, my iPhone 4 and my iPhone 4S both have the same error. Both has de iOS5.

- When I sync them to iTunes through USB in my Macbook Pro, at the end of the process it appears this message in the iPhone screen:

“Sincronización con iTunes. No se han podido sincronizar 2 ítems. Puede obtener más información en iTunes”.

I don't know the exact translation to English but it says that there are 2 items that cannot be synchronised and indicates me to see more information in iTunes, but I look at iTunes and I cannot find any information about this error.

The second error is that, from iOS5 update, sometimes when I open Dropbox app or Adjust screen, they close unexpectedly.

I hoped this errors will fix in the new iPhone 4S but... they follow occurring.

Could you help me?

Regards from Spain and I beg you excuse my poor English.

Nieves Girona