Just updated to the latest version of ACT. It seems now that two accordions on the same page causes error:
Multiple controls with the same ID 'h0' were found. FindControl requires that controls have unique IDs.
If you eliminate the HeaderTemplate, you get the same error except the ID is: 'c0'. HeaderTemplates or ContentTemplates can be blank and you get the same error. The error is very simple to replicate - just place two accordions on the same page (with HeaderTemplates).
I've found this error posted in other threads, but no solution or work around that works for me.
Any ideas?