The circ.reg function does not work properly under Version 6.0.  The problem is that the returned value of the function , circ.lm, is created using the line

circ.lm <- null
 

In earlier version of S-PLUS, a list object was automatically created with this line of code.  However, in Version 6.0, an error is returned.  To fix the problem, you may edit the function yourself, replacing the above line in the circ.reg  with

circ.lm <- list()
 

Alternatively, you may download a data dump file of a fixed version of the function:  circ.reg dump file.  Use the  data.restore function to then bring this function into S-PLUS.  It will create a new function called circ.reg.new.  If you need assistance with this, consult the S-PLUS help topics for data.dump and data.restore, and/or send me an email for further clarification.