Thread:Project:Support desk/Category not displaying in v1.19.2

any Category page just results in a blank page - as far as I can tell all other pages are displaying OK.

I assume it is being caused by an extension, but I've no idea which. Apart from those installed during install, I have added Cite, CategoryTree, DynamicFunctions, ExternalData, GoogleMaps, ImageMap, RandomImage, Renameuser, SimpleSecurity, StubManager, UserMerge, Widgets

Any idea to the cause appreciated