Could you please try the following to resolve this issue:

- Restart your machine
- Insert the Pastel installation CD in the cd Rom
- Exit the autorun screen by clicking on Exit
- Double click on the My Computer icon.
- Right click on the CD Rom drive and left click on Open
- Double click on the Products Folder
- Double click on Util folder
- Locate the ISscript10.msi folder and double click the file

Restart the machine and if needed, try running the installation again.