"Unknown error" in Outlook Express occurs sporadically when using newsgroups. The relevant Code: is 800c0133.
I tag a load of messages and then synchronize the newsgoup. When the error occurs OE6 refuses to download any further message bodies of the tagged items but is happy to download untagged items in the same newsgroup or any in other newsgroups. The ISP is adamant that there are no limitations on the amount of downloads per day and thus it must be software.