Alright, a possible breakthrough in the error and download issue.
I thought about what I stated regarding the client downloading mail and then stopping at a certain point.
On my Mac I checked the user\Zimbra\zdesktop folders where the client files (Message store files) are located and found they were 1.3 gigs of total data!
So thinking that it may be something to do with "data size" I started cleaning out my inbox inside the Zimbra desktop application. I started with all large attachments messages and then generally anything I could live without. (
I backed up my inbox by exporting it inside of Zimbra first)
Then after cleaning it up and getting the size down to 950 megs I logged out and had the client reconnect to the yahoo login once again (I did this 30 times to try and reconnect last night and today).
FYI Remember to clean out your
deleted items in order to remove the files and data size from your total message store.
And what do you know? It logged in and started downloading again! Yeehaw!
My conclusion: So it's either file size, amount of total messages in the store or it was just a coincidence that it started working again.
It's working now, I'll keep you posted on any future developments.
This client rocks...I'm going to try to get it demo'ed and implemented at my site. I'm sick of exchange. Do they have a roadmap to getting free of an exchange addiction!

If not, you guys need one.