with upgrading SharePoint 2007 to SharePoint 2010 we need to check some parts on the current farm before upgrading it. Most upgrade rules coming from installation and supportability rules of each product and in an upgrade these rules are combined. E.g. SharePoint 2007 support “Internationalized domain names”. SharePoint 2010 does not support.
What’s an Internationalized domain?
WIKI – Reference
An internationalized domain name (IDN) is an Internet domain name that contains at least one label that is displayed in software applications, in whole or in part, in a language-specific script or alphabet, such as Arabic, Chinese, Russian or the Latin alphabet-based characters with diacritics, such as French. These writing systems are encoded by computers in multi-byte Unicode. Internationalized domain names are stored in the Domain Name System as ASCII strings using Punycode transcription.
example: http://myDomainÄÖÜ or http://détaché
In a normal English installation i can’t see domains with special characters, but it’s no guarantee. In Europe and other sites in the world in multi languages SharePoint farms i see domains with special characters. With this knowledge we need to be aware of any character like (á, à, â, é, è, ê, í, ì, ó, ò, ô, ú, ü, ñ, ç, …).
In case you have such a domain in your environment we need to change it.
Reference: Technet - http://technet.microsoft.com/en-us/library/ff607742.aspx
I hope this helps.