Serbia currently has two TLDs, .rs and .yu. The .rs TLD is now replacing the .yu TLD, all .yu TLDs should be transferred over to .rs by September 30, 2009. FYI, .rs stands for Republika Srbija (The Republic of Serbia).
On March 10th, webmaster were now able to registration their new .rs domain names. Many people started the transfer process from their .yu TLDs to the new .rs TLDs. They set up the 301s, moved content, and tried to verify their sites with Google Webmaster Tools.
A detailed and long Google Groups thread has confirmed issues with Google Webmaster Tools verifying the new Serbia TLD, .rs. Googler, JohnMu said:
Thanks for reporting and researching this issue. From what I have been able to test in the last few days this most likely only affects verification in Webmaster Tools (not crawling and indexing). I've passed the issue on to the team so that they can look at it.
I certainly hope it is not an issue with the main Google crawler indexing and ranking the new TLD. It seems to me that Google has indexed many .rs TLDs already, so the issue must only be a Webmaster Tools verification issue. I suspect the issue will be resolved fairly quickly, if not, I will keep you posted.
Forum discussion at Google Groups.