I had a similar problem.
I think with the new iTunes Producer and iBook requirements following the recent updates, the process is to ignore your previous itmsp upload file and use the Publish option in iBA.
I had to get the Vendor info from my iTunes Connect account - leave the page open!
Use the vendor ID to set your process going and carry on as before filling in the blanks. I used copy and paste from iTC for the description etc or presumably you can start again.
You will need to re- fill every step and when you get to the assetts you are asked if its the same book or a new version. Version No 1.1 is in place IF you advise a new version.
I had a problem here - it said it was the same book although I had added new images and captions and corrected typ0s and out of line stufff!
An error msg said I needed to include a preview.( mine is a free book and previews were not required before) I opened iBA at the book, duplicated, saved as name-Preview and butchered lumps out to leave a fair variety over 15 pages. Back in the producer I added that preview and moved on to the book cover and screen shots. Everything was OK.
Now in iTC I have a new orange dot with 1.1 Review Pending.
I assume that all version info is retained by vendor info and if we do new versions and open it via the metadata options.. all will be in place as before the updates and asking for version 1.2
I am not saying this is Apples way - its what I did to get the book updated and back in the store.
The original or previous version will stay in the store unless and intil a review is passed.
Thanks vinnyvg! That sounds like a good work around.
Just to put it in print, I also called the iBooks-specific help phone number and emailed the support. Both were VERY helpful. The phone call, surprisingly, lasted all of 10 minutes from dialing the number, to contacting a human, to her checking into my questions. Really great.
The answer I got from both points of contact was that you actually can use the same .itmsp file. The advantage is that it retains all of your metadata, just have to delete and re-add any info/assets!
Now one of my books was made in iBA, the other was made in Pages and converted to ePub for upload through iTunes Producer. The only thing I'm unsure of now is that, unlike in iBA, you cannot specify that this is a new version. I'm trying to upload this one now. I'll post how it goes.