Problem moving WP site to new host and domain name

I am trying to move a WordPress web site to a new hosting service, while changing the domain name from domain-name.com to domainname.com using Steve Taylor’s great instructions at https://sltaylor.co.uk/blog/moving-wordpress-new-domain-server/.

I have gone throough the code very carefully changing all occurences of domain-name.com to domainname.com. I was careful to change the s:stringlength to the correct value.

Everything has gone well except for a sidebar menu not displaying and when I try to log in to domainname.com/wp-admin/admin.php. I get the login screen but, after entering the username and password, I get a blank page.

I have been at this all weekend, but am at a loss as to where to look.

Can anyone suggest where I might go from here?

Thanks,

Mike Butler