MediaWiki:Titleblacklist-custom-repeated-namespace-prefix

You appear to be trying to {{#ifexists:Template:PAGENME|view|create}} Titleblacklist-custom-repeated-namespace-prefix but are actually about to create Category:Titleblacklist-custom-repeated-namespace-prefix

If you are trying to {{#ifexists:Template:PAGENME|view|create}} Titleblacklist-custom-repeated-namespace-prefix, just follow the red link.
If this is the page you want to create, please make a request at Wikipedia:Administrators' noticeboard.