I upgraded SharePoint 2010 to 2013 using Attached Content Database method. I followed below steps
Took backup of Content database of 2010 from Sql 2008
Created New Web Application in 2013
Installed WSP in 2013 Farm solution using
Add-SPSolution "c:\example.wsp"
Restored in Sql 2012
Attached Database to the 2013 Application using PowerShell with
stsadm
Operation completed Successfully
My web application got upgraded to SharePoint 2013, but my web part doesn't work after the upgrade.
The following page is shown: