Problems downgrading gnucash?

[Dast]

Hello all,

I am trying to downgrade from gnucash 1.8.7 to 1.6.6 and I notice the
following crash when trying to open my data file.

,----[ error ]
| ** WARNING **: Unknown type: book
| 
| ** CRITICAL **: file sixtp.c: line 515 (sixtp_sax_end_handler):
|    assertion `pdata->parsing_ok' failed.
| Error: sixtp_handle_catastrophe: parse failed at 
| 
| (stack-frame 0x82bdb60
|              (parser 0x81adab8)
|              (tag (null))
|              (data-for-children (nil))
|              (data-from-children)
|              (frame-data (nil)))
|   (stack-frame 0x82ccb60
|                (parser 0x82bd6a8)
|                (tag gnc-v2)
|                (data-for-children (nil))
|                (data-from-children)
|                (frame-data (nil)))
|     (stack-frame 0x82ccc50
|                  (parser 0x82bd9e8)
|                  (tag gnc:count-data)
|                  (data-for-children 0x82ccc68)
|                  (data-from-children)
|                  (frame-data 0x82ccc68))
`----

I've searched the mailing list archives and I only found two instances
of what looks like the problem I am seeing:

http://lists.gnucash.org/pipermail/gnucash-user/2003-September/008454.html
http://lists.gnucash.org/pipermail/gnucash-user/2001-August/002187.html

Does anyone have any ideas to help me convert my file to something
usable in 1.6.6?  I tried removing the gnc:book tag and other lines
related to it without any success.

Thanks,
-- 
--Dast

 "Trust the man with the corrective lenses."
  Large Professor