EndNote X3 is not compatible with Office 2010. It is recommended that you upgrade to EndNote X4, which is compatible with Office 2010. Below is a link from EndNote on support:

http://www.endnote.com/enword2k7.asp

Faculty & Staff can purchase EndNote X4 for $35 and can be downloaded from the Faculty/Staff software download website, http://software.uh.edu/ . 

Students can purchase EndNote X4 for $79, from the CougarByte. For more information, please visit the following link:

EndNote X4 for Windows - CougarByte

For more information, contact the IT Support Center Help Desk at 713-743-1411, email support@uh.edu, or visit the IT Support Center in room 58 MD Anderson Library (in the basement). In addition, please consult the UH Get Help system, located at http://www.uh.edu/gethelp/ for answers to common inquiries.