This afternoon I download latest verison of Cosmos(link on the homepage)
P.S.: When I downloaded PearOS sourcecode I also have this error
Ok first things first, make sure you have the current source. Secondly I have found this problem when downloading my own source and the fix is really simple.
Step1 Go under the source code tree and find the iPearBoot with a cosmos logo, right click and click "Set as startup project".
Step2 Debug, but make sure release is selected.
Step3 if you still get the error, then try step 1 again, if you still get the error after that then do step 4.
Step4 Go to the source tree and right click ipear solution, and click "Set as startup project" then do step 2.
This will fix it, I believe step1 does, but I have found step 4 does sometimes as well. Hope it helps - Matt