YOSEMITE FILEKEEPER / BACKUP was the culprit ! After numerous reinstalls... NOT installing the Yosemite Filekeeper and backup FIXED the problem.  Obviously there is a bug in it that is causing this problem.  
Greetings everybody, I URGENTLY need the assistance of somebody who may have a possible solution to my problem: NEW PowerEdge2900 server, Windows SBS2003 in a default domain configuration... Dual-homed... Perc6i with 4 146GB SAS hard drives in a RAID 5 configuration...4GB ram. Have run the setup wizard with no problem... domain up and running with 10 clients on... Exchange working... printers installed... data moved into position and shares set up... etc BUT: When the clients attempt to access a share on the server (standard share of data copied over from old server... word docs etc... copied to new server, shared with EVERYONE in full control on both share level and NTFS level...) when the data is accessed through Word, for example, across the networked drive, BOTH the client AND the servers Explorer.exe process crashes and takes out both machines so they need to be force rebooted.  NOTHING shows in event logs. The clients were on a domain with the same name (businessname.local), same server name (srv1), same settings, same everything before being removed from the old domain and server and moved to the new domain and server.  They NEVER had an issue of any kind like this !!  And I suspect if I removed them from this domain and added them back to the old server, there would be no problem. I suspected it was security issue thus the everyone set to full control... am going to try to eliminate security issues completely by copying data over to a fat32 drive then back again to erase security settings that may be on files and folders.  But thought I would get the usual MS messages to inform me of access restrictions. IS is possible that the network cables could be the issue ?  Old system was 100mpbs (nics and switches) new system is Gigabit nics, and switch.  Cables are Cat5e and will replace those all tomorrow just in case.  Could it be a really bad interupt issue ?  Performance monitor shows server is doing very little. Everything else SEEMS ok (Exchange etc) ... some slow downs but expect that as the server does its piles and piles of Windows updates on itself. What other things could it be ??  Suggestions ?? MANY thanks !!
new PE2900 - mapped drive read causes client AND server to lock-up !