Deployment Solution

Getting script error 5100 during execution when running and install job within Deployment solution. Nothing in event viewer on client computer and cannot find this error on internet - any suggestion gratefully received. trying to install .NET Framework 4 via a script.

This is a pretty generic error message.  If you run this same executable outside of DS, does it work properly?  It could be anything -- try running it manually to see what errors appear if you don't use a silent install.

Error 5100 is a generic .NET setup block error. It could mean any of the following:

The user running the setup doesn't have admin privleges.
A newer version is already installed.
The OS you are installing on isn't supported.
The OS doesn't have the minimum SP required.
32-bit Windows Imaging Component isn't installed.
etc.

As I understand it, there is supposed to be a log file created. It will be in the %temp% folder on the machine with a name starting with 'Microsoft .NET Framework 4 Setup'.

I'd check that log to see if it gives any specifics to why it failed. Here's a good blog on MSDN that goes over some potential problems:
http://blogs.msdn.com/b/varungupta/archive/2010/06/22/troubleshooting-net-framework-4-install-failures.aspx