TPT15.10. The need for TWB_ROOT ?

Hello,
We are getting errors when running TPT 15.10 on Solaris 10.  Output is :
Teradata Parallel Transporter Version 15.10.00.04 64-Bit
TPT_INFRA: TPT02002: Error: TWB_ROOT environment variable is not defined.
 
However, The TPT 14.10 User Guide says:  "Replaced TWB_ROOT with the following variable: TPT_install_directory."
The TTU 15.10 Install Guide for Solaris doesn't mention it, referring instead to the TPT_install_directory.   
I believe we have installed correctly, according to the install guide.    tbuild is in the path and appears to be starting (until the error)
The 15.10 Messages reference suggests that it is still required (TPT02002)
 
So, is TWB_RROT required as an environment variable or not ?  Is an Incident warranted (doco or TTU)?
 
Thanks