While trying to open an email that is a response document, you receive the following error:
"Only plain text can be used in this type of field"
The email does not open and you cannot forward it or reply with history; however, you can reply without history.
In a few cases, this issue occurred because a doclink somehow got embedded in between the header fields of the previous email. Scrolling through the document, using a Notes 5.x client, the link was present between the To and CC field or CC and BCC fields, instead of in its respective location. It is unclear how this occurred but removing the link and re-saving the document resolved the error.
In another case, the Body field was either corrupted, or not being correctly interpreted.
The general cause for this issue is related to exceeding an address field limit. Refer to the following documents for examples:
In the case of an errant doclink, the workaround was to use a Notes 5.x or 8.x client to edit the document, locate the affected doclink and delete it. In one case, one of the address fields had extensive content, and editing the document using Notes 5.x or 8.x, and removing the content, allowed the document to be opened in Notes 6.x and 7.x. For cases where an address field contains extensive content, refer to the document references in the section above.
The case where the Body field content caused the error was reported to Quality Engineering as SPR# JGRN6CQJSQ; the issue has been indirectly fixed in Notes 8.0.
When replying to a message a doclink will be placed next to the subject field of the saved/sent message containing the document's history.