I can confirm the problem.

Experiencing same problems as well

Please make sure all files get replaced by the update. So get a fresh copy of 3.6.0 stable and extract. Remove the installation folder and override all files with the downloaded one. Please keep in mind that all core hacks gets reverted this way. Thanks.

Hello zero-24, same error also after extract fresh copy of 3.6.0 and remove the installation.

@alexred Please double check that there is no issue with uploading the files to the server.

Than please double check that this file is the same on your server: https://github.com/joomla/joomla-cms/blob/staging/libraries/legacy/controller/legacy.php

I test it in my local server, in a fresh new 2.5.28. No problem to copy file. But in your test is ok the update from Joomla 2.5.28 to 3.6.0 ?

I had already tried a entirely fresh copy of 3.6.0 before submitting my entry - same deal. I would surmise it has more to do with an incorrect entry in the database.

My guess:
It may be that some old file from 2.5 (or 1.5) is loaded instead of a new from Joomla 3.6.
Joomla auto loading try to find some lib file in incorrect directory.
After you delete old file from libraries, joomla should start working again.
You may try to find some old file in libraries/cms folder that exists but should not.

Can you compare new Joomla 3.6 extracted from zip with your copy?

For example delete if exists /libraries/cms/controller/legacy.php

Updated.
Please also check for:
/libraries/cms/model/legacy.php
/libraries/cms/view/legacy.php

I confirm the issue
Although these files are present in script.php, they are not deleted.
Once these 3 files are deleted, one can login without errors.

@mbabker
What you think?

I suppose that the problem also exists in 3.5.1 because I fixed it manually on my website a few month ago.

Ok. I have reproduced the problem. please see: #11117 (comment)

Thanks for the help so far

Deleted the three legacy files, which then allowed me to login successfully. Front end has always worked fine, just can't use admin to update anything as it will not save edited articles. Successfully updated the only 3rd party plugin, NoNumber Sourcerer

Noticed another issue with this, and other 3.6 upgrades i've done:
"Install from Web" plugin button doesn't work (or other install plugins don't activate), so have to discover the plugin(s), but even when installed they doesn't show so have to disable and then re-enable install plugins to activate them.

Additionally, with this install (from 2.5.28) while I seem to be able to access every other page, I now cannot access Global Config.
So... trying http://wisereaction.org/administrator/index.php?option=com_config
I get:

Fatal error: Call to undefined method JStringNormalise::fromCamelCase() in /home/wiseract/public_html/components/com_config/view/cms/html.php on line 210

I changed permissions from 444 to 777 with no luck.
Of course, I can edit the configuration file directly but thought you might like to know.

Also, this 2.5.28 to 3.6 threw up database errors. The database requires the following fixes:

• Table 'jos_session' does not have column 'session_id' with type varchar(200);. (From file 1.7.1-2011-09-15.sql.)
• Table 'jos_redirect_links' does not have column 'old_url' with type varchar(255);. (From file 1.7.1-2011-09-20.sql.)
• Table 'jos_redirect_links' does not have column 'new_url' with type varchar(255);. (From file 1.7.1-2011-09-20.sql.)
• Table 'jos_banners' does not have column 'alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
• Table 'jos_categories' does not have column 'alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
• Table 'jos_contact_details' does not have column 'alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
• Table 'jos_content' does not have column 'alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
• Table 'jos_content' does not have column 'title_alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
• Table 'jos_menu' does not have column 'alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
• Table 'jos_newsfeeds' does not have column 'alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
• Table 'jos_content' does not have column 'alias' with type VARCHAR(255). (From file 1.7.3-2011-11-10.sql.)
• Table 'jos_newsfeeds' does not have column 'alias' with type VARCHAR(255). (From file 1.7.4-2011-11-23.sql.)
• Table 'jos_content' does not have column 'alias' with type VARCHAR(255). (From file 1.7.4-2011-11-23.sql.)
• Table 'jos_content' does not have column 'title_alias' with type VARCHAR(255). (From file 1.7.4-2011-11-23.sql.)

On clicking the "Fix" button I get a problem with the first one:
Table 'jos_session' does not have column 'session_id' with type varchar(200);. (From file 1.7.1-2011-09-15.sql.)
from which I get the error:
Specified key was too long; max key length is 767 bytes SQL=ALTER TABLE #__session MODIFY session_id varchar(200);
only way I could fix this was to changed collation from multilingual ( utf8mb4_unicode_ci to utf8_unicode_ci )

Next one:
Table 'jos_content' does not have column 'title_alias' with type VARCHAR(255). (From file 1.7.3-2011-10-15.sql.)
then throws up an error:
Unknown column 'title_alias' in '#__content' SQL=ALTER TABLE #__content CHANGE title_alias title_alias VARCHAR( 255 ) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL DEFAULT '';

Unless you have some bright ideas with this, I'll manually work through these...

So it seems the rest of the problems associated with upgrading from 2.5.28 to 3.6.0 such as database update errors, subsequent inability to save changes to articles, are related to a multilingual install.

please test #11282

Closed as we have a PR for testing