A Google search leads to this page, which says
(Formerly James Warren Literary Agency)
Johnson Warren Literary Agency
A search on the latter name leads to SFWA:
Writer Beware has received complaints about Oak Tree Press of Springfield IL, run by Billie Johnson, who also ran the fee-charging Johnson-Warren Literary Agency. Complaints include non-payment of royalties and charging authors hundreds of dollars for "additional" print runs that are never produced. Formerly located in California, the company has recently moved to Illinois. In 2003, one author won a summary civil judgment against the company for copyright violation. (Note: Ms. Johnson's company is not to be confused with Oak Tree Press of Cork, Ireland.)
Other than that, dunno.