To address this issue, the nonstandard columns need to be removed from the hidden Workflows library.
To get to the Workflows library's setting page do the following:
1. In SharePoint Designer 2007 right click on the Workflows library and click Properties.
2. Click the Security tab.
3. Click Manage permissions using the browser.
4. Using the breadcrumb click Settings.
5. The URL will contain the following system page: http://yourSite/_layouts/listedit.aspx?List=ListID.
If the Workflows library's List ID is known then it can just be supplied to the above page in place of ListID, as a URL query string parameter, and the previous steps can be skipped.
6. The only columns that should be present are:
Checked Out To.
The management of content types is not allowed either. Looking at a working Workflows library's settings and comparing them to the settings of a broken Workflows library is a good way to validate the state of the Workflows library in question.
The Workflows library is hidden by default and facilitates a very specific function. It should not be treated like a normal document library where users go into the library and add columns or modify other settings.