When you select Typeset, Preview PDF and see a message of the form:
Error while attempting to execute [C:\Program Files\Adobe\Reader\AcroRd32.exe] "C:\swp55\docs\sample.pdf"
The system cannot find the file specified.
it is often assumed that creating the PDF file failed. However, this is not the case. Instead, the PDF file has been created but SW cannot find the PDF viewer program and displays this message. Perhaps you updated your version of Acrobat or Acrobat Reader after SW was installed.
See http://www.mackichan.com/techtalk/725.htm for the steps to update SW so it uses the current PDF viewer program.