ActiveSync is supported only on Windows XP.
For Windows Vista and Windows 7 you need to use Windows mobile device center.
Please download Windows mobile device center and install.
Then install RhoElements on your Windows 7 desktop and then try to install on your mobile device via Windows mobile device center.
Alternatively, you could bypass ActiveSync or WMCM by simply copying "RhoElements 188.8.131.52 Runtime.CAB" file directly over to a SD card. Insert the SD card in the device and launch the .cab file from "Storage card" folder.
The RhoElements .CAB files are located in "C:\Program Files (x86)\Motorola RhoElements v1.0\Windows" folder.