An error has occured

org.apache.cocoon.ProcessingException: Attempted to process incomplete pipeline.
<map:serialize type="html"> - context:/file:/Volumes/data1/wd/projects/Hearthstone/HAM/site/prod/webapp/sitemap/main.xmap - 48:27

Cocoon stacktrace

Attempted to process incomplete pipeline.
context:/file:/Volumes/data1/wd/projects/Hearthstone/HAM/site/prod/webapp/sitemap/main.xmap - 48:27<map:serialize type="html">
context:/file:/Volumes/data1/wd/projects/Hearthstone/HAM/site/prod/webapp/sitemap/main.xmap - 44:49<map:transform>