Tanya - sorry for the delay in your receiving a reply. Ricochet is a Gantry 4 template, so you don't need Gantry 5 installed (I've now uninstalled it). You have Gantry 4.1.29 installed which is way out of date - so I have now updated it to Gantry 4.1.40 for you and now template manager works again.
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