Error in Web parts after SharePoint platform upgrade

Using MOSS 2007 web part code, i have re build the VS 2010 SharePoint project. After deploying the webpart, i was getting error.

Solution:
I have added below tag in web.config

SafeControl Assembly="MyCustomWebpart, Version=12.0.0.0, Culture=neutral, PublicKeyToken=bdb4a6220fe9433c” Namespace="MyProject.UI.WebParts” TypeName="ListItemReport" Safe="True" SafeAgainstScript="True"

SharePoint remove and repair the broken Web Part

Some times, you will see some webparts shows error, but will not able to delete that web parts.
Using below url, you will able to delete the webparts.

http://SPO/default.aspx?contents=1

You will see all error-ed webparts, select webpart and delete.

Error occurred in deployment step 'Activate Features': Cannot start service SPUserCodeV4 on computer

Root Cause: Microsoft SharePoint Foundation Sandboxed Code Service is stopped.
Solution:
Open Central Administration site
go to System Settings
lick on Manage Service on server
Check to see if Microsoft SharePoint Foundation Sandboxed Code Service  is running, it should be stopped
Start the service and try deploying the Sandboxed solution