Top menu styling is lost when upgrading Joomla

If you are certain that makes me uncertain because I know that menu class suffix should be " nav" and that is all.

i have exactly the same problem and mine is nav

Send link so we could check

sorry been in meetings all day

i had actually deleted the site but just done a fresh instal and updated and now i get

Fatal error: Call to undefined function mb_internal_encoding() in /home/renewabl/public_html/dir/components/com_k2/helpers/route.php on line 61

im not bothered about using k2 so can delete if that easier

That new error you get may be due incomplete copy. Upload whole ...hot_start.zip and unpack it on server directly using cpanels file manager. That way you are sue all files are there

thats what i did and i have also copied over the com_k2 files afterwards as thats what i thought went wrong

i will delete it all again in the morning and start again