Hello.
Yes indeed, I made yesterday, complete test of the structure and plugins and it seems that error is caused in conjunction with WP Cerber Security which is also crucial for this site as Download Manger. I think the most important part is that:
WPDM\\User\\Login->verifyLoginEmail(NULL, ‘Test user’, ‘Test pass’)
As I said earlier, the previous version 3.2.86 – worked without any problem.
I hope that it’s going to be cured, since the site is offline now. WP Cerber and Download Manager made it workink as a charm.
Thanks in advance for the help.