Update
Mike Mongeau, a forum moderator at Microsoft Answers says as follows, I would point out the error I experienced was with one of the custom fields and not date but I think the date field will be the most common of the two. If this doesn’t work for you move beyond the update section for another potential remedy:
Everyone: I’ve done some digging and believe I know the cause behind the error code. It seems Google contacts allows for birthday fields of many formats, including something like Month, DD, YY. So, a birthday like “October 17, 11″ will cause a sync failure. The phone sees the year not as 2011, but actually as year 11. It naturally balks at this. Here are some other notable findings with this:
What’s odd is that Google doesn’t allow you to enter birthdays in this format (at least, not any longer). Instead, to get myself into a “bad state” I had to import my contacts with the birthday field entered like this. Meaning you guys either (1) imported your contacts or (2) had entered these birthday values in some older interface of Google’s contacts.
This isn’t a regression. Any contacts with this birthday value will, in fact, fail to sync pre-Mango – just the error code isn’t shown.
To fix: simply edit the birthday field of your contacts in this format (or delete) to be MM, DD, YYYY. Finally, remove and re-add your Google account.
The Problem
After installing Windows 7.5 (Mango) on my HTC Mozart Windows Phone all worked well for a couple of days. I noticed that Gmail was sometimes not synchronizing but put it down to poor cell coverage. I began to receive calls showing the number and not the contact, and then, when trying to make a call one day I found all my contacts missing.
I searched for solutions online. I found similar complaints however these were for the earlier version of Windows 7, 7.5 better known as Mango had only just been released and surely, the problems in the older version of the software had not been brought forward to the new?
They had.
I followed several suggestions on forums and blog posts but failed to solve the problem. I raised my question on Microsoft Answers but that, at time of writing this still offered no solution. Strange name for a website “Microsoft Answers” because they never bloody do.
The Solution For Me
To understand the solution it’s best you know what I think the cause is first. That way you may find a better solution for your own particular set of circumstances: I believe the cause is WP7′s inability to understand Gmail’s Custom field used in their contacts list to store miscellaneous information. At first I thought it might be some of the character sets in use in my contacts. I have Asian, Eastern European, Russian, Greek and several other contacts all of whom have shared their Vcards with more information in their own characters, but after summarily deleting these Microsoft remained incapable of importing them.
Some had large quantities of information, so I targeted these next, but still, Microsoft could not import them.
I was left with a few that had HTML tags which I removed and still Microsoft could not import Gmail contacts.
I then removed all Custom fields in Gmail and at last, Microsoft managed to import the records. So this is my solution and these are the steps I took to successfully import Gmail Contacts into my Windows 7 HTC Mozart Mobile Phone.
- Export all Gmail contacts to Outlook CSV
- Open CSV in your editor (I used Excel)
- Delete the Notes column (in Excel click the top of the column and hit delete)
- Save your CSV
- Import CSV into Windows Live Contacts (this maybe unnecessary but I figure if Microsoft Phone cannot read Microsoft Windows Live contacts then I may as well have bought brick)
- Delete all contacts in Gmail (Don’t panic, Gmail has an easy to use recovery feature if you screw up)
- Export from Windows Live to CSV
- With Gmail Contacts empty, use Gmail’s import utility to import the contacts you exported in the above step from Windows Live
- Go to your Microsoft Windows 7 Phone and Synchronise
That did it for me; I hope it helps you.
Epilogue
Chrissakes Microsoft get this sorted. I can see people dumping your phone because of this one tiny-itty-bit of a problem and your choice to ignore complaints exacerbates the rush for alternatives. I decided against iPhone because I have Windows everything around me, I chose not to go for a Galaxy S because a friend complains the O/S and programs often crash. I am happy with the decision but frankly, if I can’t get access to my contacts the iPhone or Android make much more sense.
Do you keep hearing a voice message warning you to clear your cache and cookies? I don’t, but my father experiences it and when he described it I could not believe it. Why would such a pointless and stupid message be played every time you opened the browser? 
My walks, hikes, rambles, kloofing, backpacking, excursions, treks, and walkabouts return to the starting point making it easy to plan your day.