Without Run as Administrator, can you access the UNC by IP instead of server name? IP uses NTLM auth whereas name uses Kerberos auth. That could be your BOI workaround (but wait there's more).
If it works it means tighter Kerberos security. There were several changes in Windows 8 and 2012 for Kerberos so possibly one of those is affecting you. These are controlled either through Active Directory Users and Computers or Group Policy. IT guy could check -
http://goo.gl/gtRzo
Having said that, there are 2 client side settings that could be the culprit instead:
1) Add an entry to Local Intranet zone (not Trusted zone)
a) Goto Control Panel / Internet Options / Security
b) Click on Local Intranet / Sites button / Advanced button
c) Type the UNC or just type file://<server name> (without the <> )
2. Goto Control Panel / Internet / Advanced tab
a) Scroll down to Security settings
b) ""Enable Integrated Windows Authentication"" should be checked
Hope that helps. I do have 1 question - were you logged into the local machine instead of the domain per chance?