Answer:
Assuming you Installed the Sun JRE as part of your Teradata 12.0 Express Environment, you may need to configure this.
Within your TD12 environment open up a Teradata Command prompt and use "cufconfig" with the -o (output to screen) option.
Check if the JREPath is set in a manner similar to that below.
JavaLibraryPath: C:\Program Files\NCR\Tdat\tdconfig\jarlib\
JREPath: C:\Program Files\Teradata\TDJRE\12.00.00.00\
JavaLogPath: c:\Temp\
JavaEnvFile:
JavaServerTasks: 20
JavaVersion: 0x10004
JavaBaseDebugPort: 8000
JSVServerMemPath: C:\Program Files\NCR\Tdat\TdTemp\jsvsrv\
MallocLimit: 33554432
If JREPath is empty or points to a non existent directory, you will need to install TDJRE.
Go back to your Teradata 12.0 Express Instalation CD/Download and run setup.exe again to get to the Install Additional Sfotware page.

Once you can see that TDJRE is installed you need to let the database know where it is.
One approach is to set the Environment Variable (Start -> Control Panel -> System -> Advanced -> Environment Variables) TD_JAVA_HOME to the address of the corresponding installed JRE (like C:\Program Files\Teradata\TDJRE\12.00.00.00) then run "cufconfig -i -o" (remember to open a new Teradata command prompt to let new Environment Variables get loaded).
Alternatively you can create a small text file within the working directory of the Teradata command prompt, say setJRE.txt and insert the lines:
JREPath: C:\Program Files\Teradata\TDJRE\12.00.00.00\
Then use "cufconfig -f setJRE.txt" to change the JREPath value.
If the JavaBaseDebugPort does not have a reasonable value (say 8000) you can repeat this process with a line like:
JavaBaseDebugPort: 8000
Once the configuration presented by "cufconfig -o" matches your physical configuration restart the DBS with "tpareset -f be".