D7100 needs ACR 7.4 which is available with PSE 11 : http://helpx.adobe.com/creative-suite/kb/camera-raw-plug-supported-cameras.html
RAW files from this camera will not work in PSE 10
Either you need to upgrade to PSE 11 or use DNG converter 7.4 to convert your files to DNG format so that they can used in PSE 10
Photoshop Elements 10 does support Adobe Camera Raw 6.4.1 to 6.7 and minimum requirement for Nikon D7100 is ACR 7.4.
Camera Raw plug-in | Supported cameras
Camera Raw-compatible Adobe applications
You need to upgrade to PSE11 or can convert the NEF files to DNG and import into PSE10.