Upgraded and now I can not edit my theme at all, on saving anything, I get an EX0 error message. 

Anyone have any hints as to what i need to edit?

From 4.0.x to 4.1.x?

Yup.  I told the upgrader initially not o automatically fix the theme (Big mistake I gather), now I can't edit it at all. 

Any ideas?

4.0 themes does not work for 4.1. Before you upgrade IPS4 always check this section https://community.invisionpower.com/index.php?app=core&module=system&controller=plugins&do=diff if you have added custom themes.

Wow, lots of stuff, and I don;t really know what any of it means.  

Nothing easy to do to fix it?

Is this a custom them from a theme developer or one you made? if you only used custom.css there shouldn't be any issues, if you altered templates, then you would need to revert those templates and re-apply your changes, or update the changed code in the altered templates.

 

 

7 minutes ago, wmarcy said:

Wow, lots of stuff, and I don;t really know what any of it means.  

Nothing easy to do to fix it?

Only a lot of stuff if you made changes to any of the templates/css files shown

Best way is to revert any templates you changed and re-do all the changes you made again (assuming you can access that)