Upgrade from 2.20 to 2.40... failed

Hi all!

I have tried to upgrade my store from 2.20 to 2.40... but it is failing miserably until now.

I have made backups of everything before I started... but my idea is not to go back to the old version until I have tried everything.

In my last try, I did the following:
1) Closed the site while doing all backups.
2) Executed Script upgrade to 2.30 on DB
3) Executed Script upgrade to 2.40 on DB
4) Saved Settings.txt and InstalledPlugins.txt files like advised.
5) Removed all 2.20 version files.
6) Copied new 2.40 version files.
7) Restored Settings and InstalledPlugins.txt.
8) Restored the uploaded images directory.
The result?
The front store fails to open, I get the usual "Store Closed" message... not a weird result, because I closed the site before starting the upgrade.
But when I try to go to my admin page, I enter:
http://www.mystore.com.ar/admin/
And I get the page: http://www.mystore.com.ar/errorpage.htm?aspxerrorpath=/login
We're sorry, an internal error occurred that prevents the request to complete.
Our supporting staff has been notified with this error and will address this issue shortly. We profusely apologize for the inconvenience and for any damage this may cause. You might want to try the same action at later time

So, I am in a dead end now... I cannot enter the admin, nor reopen the site...

Any recommendations?
Thanks!

To find out what went wrong you need to turn off the custom errors mode.
1. Open web.config file
2. Find out the following line <customErrors defaultRedirect="errorpage.htm" mode="RemoteOnly">
3. Replace it with <customErrors defaultRedirect="errorpage.htm" mode="Off">

Thanks for the quick reply.

Here it is:

Source File: ..\htdocs\Views\Widget\WidgetsByZone.cshtml    Line: 5

The controller for path '/' was not found or does not implement IController.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Web.HttpException: The controller for path '/' was not found or does not implement IController.

Searching through the forum, I did this:
https://www.nopcommerce.com/boards/t/10969/nop-20-plugin.aspx?p=4#51318

And apparently it is working now... will let you know if anything more arises...

Thanks! :-)