I am not using that soft, but I will try to give you some general unix advices:
Are you shure that you have directory /home/cad/ ? Check it.
Next, set correct permissions for that directory (under root):
cd /home; chmod 711 cad
Next check if there is such file:
cd /home/cad/ ; ls -al .cdslog
If you will see:
-rwxr--r-- 1 cad users 0 Feb 27 11:58 .cdslog
then all Ok, but if you will see owner "root" - you will need to change file owner, or delete this file under root.
Next you can try to create this log file by yourself (under user cad):
cd /home/cad/ ; touch .cdslog