Thank you for the advice but I still could not get Flex Builder 3 to compile my .swf correctly - I'm new to Flex Builder so it is probably entirely my fault.
However I found a download of the original Flex SDK 2 Hotfix 2 (which to lc-customisation instructions refer to) so I De-installed Flex Builder 3, installed Flex 2 Hotfix 2, and used the Flex 2 command line to compile the new workspace-theme.swf file.
This then worked correctly when re-built into my customworkspace-client.ear file.
I'm happy to find a solution, but it is a shame that Adobe do not provide instructions to customise LC ES Workspace using Flex Builder 3 as that is now seems the only version available to download or purchase.
At the time the documentation was written, only Flex Builder 2 was available. Agreed, that instructions should include Flex Builder 3 as that is what is available now. We'll raise a bug to get that resolved.
YOu can compile using Flex Builder 3 by changing the compile version in Flex Builder 3 (which uses Flex 2 SDK (hotfix 3, which includes hotfix 2).
To compile using Flex 2 SDK in Flex Builder 3:
1. Right-click your project and select Properties.
2. Select Flex Compiler.
3. In the Flex SDK version pane, select Use a specific SDK and select Flex 2.0.1 Hotfix 3 from the dropdown list.
4. Click Apply and then OK.
5. Compile as you would normally. Now it will use the Flex 2.0.1 (hotfix 3) SDK for that project.
As I'm only using Flex to compile changes to the Workspace Theam .ear I've written a .bat that automates rebuilding it from my manually edited .css file and images using the Flex 2 SDK which only takes 2 minutes to run.
I spent some time playing with Flex Builder 3 but it did not seem to offer much advantage over doing this as the above method.
What I'd really like is a way to edit the whole Workspace Visually using a graphical type desigener tool as the way I'm doing it now involves a lot of trail and error in terms of getting changs to graphics and colours to line up correctly. Ideally I'd like to be able to alter the size and layout of some of the containers as well.
It did not seem to me that Flex Builder was able to offer this, although as I said I'm very new to it. Do you know if there is any tool which can edit the whole Workspace 'off line' in a visual way ?