The v10.6.7 combo update includes MAS bug fixes that may help.
Restart your Mac after the combo is installed. It's ok to do this even if you are already running v10.6.7.
For iTunes. From the iTunes menu bar click Store / View My Account / Edit Payment Information. Make sure the Security Code and expiration date is available then click Done.
Buen dia Aguamala. Saludos desde Monterrey.
Do not waste your time or your bandwidth with the suggestion above to download the huge file that the affluent gringa is suggesting. You already have the MAS that the update combo installs and wasting time with that is not likely to help you at all.
Do you have Infinitum with Telmex? I had many such problems downloading things in iTunes when Telmex was my internet provider. One day things would be OK and the next day nothing would download for weeks at a time. Unfortunately we do not have many choices here in Mexico. I solved my problem first when I switched my internet service to CableVisión. And more recently Axtel has installed a fiber optic network in the Zona Centro here in Monterrey and I now have service with 10 megas.
I think that the issue is more the connection that the two apps; Mac App Store and iTunes.However, do take her advice and sign into your account in the iTunes Store and make sure that all the information is correct, especially the bank card information. (She has no idea that most domestic bank cards in Mexico do not have a 3 digit security code.)
The other thing is perhaps changing your DNS service. The best way to do this is in the configuration of your modem/router. But you can sometimes do it in Sys Prefs/Network and it will over ride the ISP settings in the router. I can help you with this if you need help.
I use OpenDNS, but folks are having success with connection issues by using Google Public DNS also.
Google Public DNS
Before I begin to download v10.6.7 combo update (thanks Carolyn), and like last resource today I speak with my internet provider and they told me (to begin) to reset my modem. They told me how to do this step by step. So I did it and now can acces App Store and iTunes correctly, TG!!
Like a side note, yesterday was released adobe lightroom 3.4.1 update and I was having problems to download the update because the website it was very slow and appears a message of error that the server it was unavailable. Today it was the same error until I reset my modem and I was able to download this update quickly!!
CAROLYN: thanks for your input!
DAH-VEED: Gracias, creo que tu info será útil si vuelvo a tener problemas con mi modem. Saludos desde Tijuana.
Well, thaks everyone for your help!