UPDATE: I gave up on this approach and moved back to Eclipse Europa 3.3

Much to my dismay, there were just too many bugs trying to get FB to support 3.5 correctly. I had it mostly working, but there are unresolved issues with the ProblemManager Class that caused consistent "internal build error" messages and generally completely unacceptable error reporting.

I don't know about you but the scope of my Flex work is such that I need top-notch error-reporting. And I really don't like having to apply multiple patches to get my IDE to a half-functional state.

If you really need Eclipse 3.5, you should give the open source AXDT a shot. Unlike FB, it works out of the box. And installs like a regular eclipse plugin. WTF can't Adobe do this???

The problem with AXDT is it is not quite finished. It still needs code-completion features, debug features, etc. But it's OSS and I really hope it gets the rest of the features it needs, because I do not want to depend on Adobe any longer. They've proven themselves to be incapable of maintaining their own software for Linux. A big screw you to the execs at Adobe who are keeping us linux Flex developers hanging on by a thread. Don't forget we represent some of your most hardcore coders! Either cut off development or do it right, huh?

With that said - if you are nuttier than I am and want to get FB on Gallymead- keep reading.

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This was a bit of a process, but it seems to finally be working.

Just upgraded to Lucid 10.4.

Installed Eclipse 3.5 via Synaptic
Installed Flex Builder

Followed the solution here but had to make two changes:

1) Change the version number in the filename of each copied file from the patch. The ending number should be 257568.

So, from the patch directory: BTW, you may need to change these: you should be copying into the $FLEX_BUILDER_INSTALL/eclipse/plugins dir.

2) nano /usr/lib/eclipse/links/com.adobe.flexbuilder.feature.core.linux.link and put path= before the location - ie, prepend the string.

3) To get Flex Builder to show up in menus, I had to run eclipse -clean and start a new workspace

4) And then to get Flex 4 SDK working, download it from here, copy it to the sdks/ directory and enable in Eclipse preferences.

5) When compiling for Flex 4 locally, I had to use compiler flags -use-network=false and -static-link-runtime-shared-libraries=true. I also had to make the minimum flash player version 10 ( I didnt have v9 installed, and it wouldn't degrade gracefully; instead I got compiler errors. )

6) Deal with the really crappy Eclipse plugin, specifically the issue with ProblemManager. It'll give you innumerable and useless "internal build errors" and "1131: Classes must not be nested" errors. I've seen patches for this but none worked for me. So I'd highly recommend doing two things if you have issues here: Clean your project by going to Project > Clean in Eclipse, and if you want to really know what's going on, just use mxmlc and compile at the command line.

7) Begin the ugly process of migrating your app from Flex 3 to Flex 4. A few quick pointers:
- CSS namespace issues
- Application.application issues
- RSL linkage issues

8) If you're like me, waste a few hours then realize it's not worth porting your Flex 3.5 app to Flex 4 until you are ready to do a major refactoring on it. The costs are too high and the gains too little. But I will build all new apps in Flex 4, and will eventually the old ones over. But no reason to rush it.

More info:
http://blog.mandalatv.net/2007/06/flex-securityerror-error-2148-while-ac...
http://forums.adobe.com/message/2755876
http://help.adobe.com/en_US/flex/using/WS2db454920e96a9e51e63e3d11c0bf66...
http://butterfliesandbugs.wordpress.com/2009/07/14/rsls-on-my-default-in...