RX 5.7 - Error generating HTML

All of a sudden most of my content gives the following error when I try to publish or preview it in Rhythmyx 5.7:

An error occurred generating HTML from XML using the "" style sheet for the request submitted by session id edef8f89e5548f1bdd1956494fc564c535ad77b4.

Exception com.percussion.cms.objectstore.PSInvalidContentTypeException:
An invalid content type id was supplied to an operation: navimage Message: An invalid content type id was supplied to an operation:
navimage com.percussion.cms.objectstore.PSInvalidContentTypeException: An invalid content type id was supplied to an operation:
navimage at com.percussion.cms.objectstore.server.PSItemDefManager.contentTypeNameToId(Unknown Source) at com.percussion.fastforward.managednav.PSNavConfig.<init>(Unknown Source) at com.percussion.fastforward.managednav.PSNavConfig.getInstance(Unknown Source) at com.percussion.fastforward.managednav.PSNavConfig.getInstance(Unknown Source) at com.percussion.fastforward.managednav.PSNavAutoSlotExtension.processResultDocument(Unknown Source) at com.percussion.data.PSExtensionRunner.processResultDoc(Unknown Source) at com.percussion.data.n.o00000(Unknown Source) at com.percussion.data.j.o00000(Unknown Source) at com.percussion.data.j.o00000(Unknown Source) at com.percussion.data.kd.processRequest(Unknown Source) at com.percussion.server.PSApplicationHandler.processRequest(Unknown Source) at com.percussion.server.gb.Ò00000(Unknown Source) at com.percussion.server.gb.run(Unknown Source)

Any help would be appreciated,
Ken