Synching issues

Hi
I'm trying to synch an iPhone in iTunes but am getting the apparently very common error -50. iTunes is synching Mail, Contacts and Calenders but then giving me the -50 and refusing to go any further. Driving me nutzzzz!
Any help appreciated.

OK.
1. Mac (which one & version of OSX) or PC (which version of Windows)?
2. Which iPhone? Which version of iOS?
3. Which version of iTunes?
4. Have you tried a different cable and USB port?
5. Are you able to buy and download content OK in iTunes? (even free stuff)
6. Are you able to buy and download content OK on your iPhone? (even free stuff)
7. Are you using the same Apple ID on both iTunes and your iPhone?
8. Has this iPhone ever synced OK with this instance of iTunes on this machine?
9. If you get content on your iPhone are you able to download that content successfully in iTunes?

Synching i phone

Thanks for getting back.
Mac Pro 2X2.66GHz Dual Core
Version 10.6.8
iPhone 4
OS7.0.4
iTunes 11.1.3
Tried different cable and USB port
Cannot buy on iTunes Store. Error 5002
I am able to purchase on the iPhone
Same ID on both
I have synched before no problem.
I can download to the phone no problem. Not sure if this is what you mean.

Thanks again

You're problem is that iTunes cannot download from the store.

The reasons can be plentiful.

First turn of 1 click shopping if you have that, then empty your wish list if you have that then log out of your ID in iTunes and quit it completely.

Now restart iTunes and log in. try to download previously purchased items or something new?

Do you still get the 5002 error?

No good. I'm still getting an error -50 when iTunes starts up and also when it tries to synch and the error 5002 when I try to buy in iTunes. I turned off 1Click by re-setting cache. Was this right?

Resetting cache?

5002 and -50 are both iTunes purchasing errors. Do you have a working Internet connection?

Try removing and re-adding your payment method

It seems to have cured itself mysteriously??? I have an older system on an ext drive and tried to use the iTunes on that but I was still getting error-50. But when I re-booted into my main HD all was fine. I have no idea why. I had tried changing my payment method earlier but no luck. Anyway I'm up and running again at least for the time being. I suspect it has to do with dodgy USB connections. The reason I suspect this is that when I use a USB wi-fi dongle it drops the connection regularly after being idle for some time and I need to remove and replace it to re-connect. I read somewhere that my iTunes problem could be the result of faulty USB hardware.
Anyway thanks a lot for your help