2) Issue: Features developed for SP2007 are not getting deployed in SP2010 and the error is "Invalid Type definition in the elements xml"
Description: Issue is a bug in WSS, due to which several users coded the elements xml for a event receiver with Type parameter as integer value. This value need to be a Enum value and SP2010 got it fixed due to which all the earlier elements xmls with integer values will fail to deploy.
Solution: Replace the integer values with the appropriate enum values in the elements xml and deploy.
3) Issue: Left menu is not visible in Internal layout pages when not visually upgraded.
Solution: Got it clarified from product team that this is by design as the sharepoint 2010 applies a minimal master page to the upgraded sites before the visual upgrade.
a) Sharepoint sites having PageViewer webpart with html pages as sources will show a Save, Cancel dialog box.
b) Sharepoint sites with flash and silverlight objects displaying a Save, Cancel dialog box.
Description: This happens in windows 2008 R2 due to the IIS security restriction for HTML pages.
Solution: Go to SP2010 Central Admin --> Application Settings --> Manage webapplication settings. Select the webapplication, edit the general settings and select the option "Browser File Handling" as Permissive