To have default client letter in print, you need to enable it in the preference settings.
In old version of myTaxExpress software, you need to change two file names inside mytaxexpress installation. For example of myTaxExpress 2013 software,
1. In folder c:\mytaxexpress-efile\mytaxexpress\2013\pdf
change file name from "t1_clientletter_example.pdf" to "t1_clientletter.pdf"
2. In folder c:\mytaxexpress-efile\mytaxexpress\2013\xml
change file name from "t1_clientletter_example.xml" to "t1_clientletter.xml"
then print the tax return again, it will have default client letter printed out.