Migration from VS 2010 to VS 2015 Problem

We recently just migrated our projects from VS 2010 framework 4 to 2015 FW 4.6.1.

Once I open the project I get tons of errors mostly for things which should work.  Error such as in code behind it doesn't have access to objects on them .aspx page and also none of the controls on the .aspx page are accessible from the code behind. This is pretty much for every object on every page. We have spent days trying to resolve with no luck. Does some references not carry over when converting?

Any suggestions would be appreciated.

thanks