Hi,
In every minute ACS software simulate an authentication packet to tacacs+ and radius process to make sure that these processea are running properly. This will happen regardless of whether you tacacs or not. If you want to turn it off , you can do the following:
System Configuration --> ACS Service Management --> Turn off Test Login Process
My approach would be to analyze why tracacs+ process if failing. Look at the windows evenviewer, and csmon log. If nothing points to the write direction, then turn the full logging on and generate a package.cab file as described by the following link to get further help from TAC:
http://www.cisco.com/en/US/products/sw/secursw/ps2086/products_tech_note09186a00800afec1.shtml
Thanks,
Mynul