This problem has come up in multiple threads enough times that it needs its own thread.
Inventables is working on a version of Easel Local that can auto-detect the COM port where your Arduino is installed. This is a work in progress, and doesn’t work for all situations, yet.
Sometimes you can connect one time and then nothing else will connect after that. This is usually a situation where the COM port is left in an undetermined state which prevents its use until the COM port is released by a manual process, either re-booting the computer, or a disable/enable cycle on the COM port in question. One way to free the port is to unplug the USB cable from the Arduino and then plug it back in.
If this is your situation the first thing to check is the version of Easel Local. If it is a version greater than 0.2.2 then you have the auto-detect code.
If you want to try Easel Local without the auto-detect code then uninstall Easel Local and then download and install version 0.2.2 to see if that corrects your problem.
Version 0.2.2 can be found here: http://s3.amazonaws.com/easel-prod/paperclip/sender_version_windows_installers/11/original/EaselLocal-0.2.2.zip?1445874573