SharePoint 2010 custom workflow error

I want to add a custom workflow to custom sequential workflow using VS 2010 c#.

I followed the instructions from this link : http://msdn.microsoft.com/en-us/library/hh824675(v=office.14).aspx ; I got this error -

Error occurred in deployment setup 'Retract Solution' : This required project property is not found or has a value of null or empty string: basePackagePath.

I have searched a lot on MSDN but did not find any solution.

What am I missing?

Thanks.