Hi, 

Gnus backend is nnml with "(setq nnml-use-compressed-files t)"

when calling function:

(gnus-summary-goto-article
         "<201012201809341712361@163.com>")

here, "<201012201809341712361@163.com>" is a message-id of a exist
article, which is compressed by nnml.

will print error message:

Couldn't fetch article <201012201809341712361@163.com>


the attached patch for fix it.