I am experiencing similar issues already reportwed on this Forum with JChem for Excel (188.8.131.521 on Windows 7/Excel 2010). I have had no issue so far but on starting Excel yesterday, the Jchem for Excel tab has disappeared.
When I look in the option tab, the Add-ins section shows JChem for Excel disabled. Looking into the COM add Ins shows the JChem options unchecked. If I try to check both boxes, my selection is not kept.
I have removed/reinstalled JChem for Excel but this has not helped and reading through similar issues has not helped so far.
Any help would be appreciated,