downgraded server from 5.2 to 5.1, everything dumps core now.

[Peter]

Hello,
   I was doing an upgrade to several servers, and one of them I 
accidentally cvsupped from RELENG_5_2 to  RELENG_5_1, did a normal 
buildworld/kernel, install kernel/world, and lastly a reboot.  When I 
realized that I had accidentally downgraded, I tried to upgrade, cvsup 
ran fine.  But now buildworld, and tons of other commands 
[w,config,man,ifconfig,etc.etc.] dont' work, or just core dump on me 
with "Bad System Call".
   Question:  Even though I downgraded, the system should function 
right?  I ran through the normal steps of buildworld/kernel, then intall 
world/kernel, all of these  ran fine and I had a final " && reboot".  
Upon reboot, httpd [apache], mysql, sendmail and tons of other apps are 
core dumping now.  I can't rebuild world to 5.2, because, well the apps 
are core dumping on me.  
  I do 'ls -l /boot/kernel' and 'ls -l /bin/any_app', the modification 
dates are within several minutes of each other, hence I'm sure that 
kernel, and world got built with same sources.  Tomorrow I go to server 
room and do binary upgrade to 5.3 BETA 4, but overall this has been 
driving me nuts, as to why it won't work... Any suggestions/ideas much 
appreciated.

---Peter---