TLF 2.0 is not a drop-in replacement into Flex 4. To even get it running changes are needed to Flex 4.0.T wo files need to be replaced in Flex 4 and spark.swc needs to be rebuilt. The files, FTETextField.as and CSSTextLayoutFormat.as, are available for download here.
These changes were tested with Flex 4.0 SDK build 14159. I believe the same changes will work with Flex 4.1. To rebuild Flex with these changes:
1) From http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4 download the “Open Source Flex SDK” you wish to modify.
2) replace the two files with the above modified versions.
3) run “ant -q main” in the frameworks directory
4) replace spark.swc with the one you just built.
There are other known issues. The biggest one is that TLF changed selection to permit inclusion of the final paragraph terminator in the selection from the selectAll API. This gives more consistent highlighting but caused some problems for Flex code. Fixes for this issue are not available for 4.0/4.1.
UPDATE For Flex 4.1
The changes for Flex 4.1 are to the same two files but the source files have changed in the Flex SDK. I posted 4.1 versions here: http://blogs.adobe.com/tlf/files/2010/08/FlexFixes41.zip
I’ve also seen the problem with building datavisualization. I solved by copying manifest_datavisualization.xml to manifest.xml in the frameworks/projects/datavisualization directory.