The side-by-side configuration error appears to be a very rare issue. Users should be able to get it resolved by uninstalling the software, deleting the .ini file and reinstalling the software. The problem is most likely caused by SAP2000 installation getting corrupted.

Below are the steps you can take to try to take to resolve the issue:

(1) Uninstall the SAP2000 V15 program through the Control Panel.

(2) Delete the SAP2000v15.ini file in the user settings folder. Depending on the operating system, the local settings folders are:

Windows Vista/7 - C:\Users\[UserName]\AppData\Local\Computers and Structures
Windows XP - C:\Documents and Settings\[User Name]\Local Settings\Application Data\Computers and Structures

(3) Download the latest standalone installation for SAP2000 V15 from the Customer Support Portal at https://support.csiamerica.com

(4) Reinstall the program using the setup files downloaded as above.

The following Microsoft Knowledge Base Article has some additional information on the subject:

http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_programs/how-to-fix-side-to-side-configuration-error/e4dae74c-8e7e-434f-aec8-dd1462f8231b