I have to point out that I use Adobe Flash Professional CS4 in integration with FlashDevelop v. 3.2.1.RTM
Do you use a compiled library like .swc ?
If you have just plain .as classes within your project try to run cache cleanup within FlashDevelop:
Tools > Flash Tools > Rebuild Classpath Cache
The caching stays the same after doing a rebuild to the classpath, but thanks for the help.
I think it didn't work because it is a IDE project and yet, the compilation happens in Flash not in FlashDevelop.
Another thing is that it happens only with this .fla and not in others. The corresponding class resides in a library that contains only .as .
Can you think of a way to rebuild the classpath cache in the IDE itslef or that there is no diference between the two?
A solution was found.
It appears that in a project that contains several SWFs that use the same base class and load to the same application domain (which was in my case), the first SWF that contains the base class, determines it for the following SWFs. It means that when you change the base class, you should compile all the other projects that contain it.
It's that simple, why didn't I think about it before...