I installed an older compiler-version (here 6.2.1 or 6.4.0) in the Studio (CE) 6.6.0 and 6.9.0 and chose that version
for compiling a subreport. The compatibility setting was also 6.2.1. JDK compliance is 1.6.
After restarting the Studio and compiling the subreport different errors appear:
An internal error occurred during "Building report!".
I tried to add that library but got another message:
An internal error occurred during: "Building report".
java.lang.NoClassDefFoundError: Could not initialize class
When using the old version of the Studio(!) 6.2.1 it works but that is just a workaround.
By the way:
Using "6.6.0 (current)" instead of "always the current" (Studio 6.6.0) does not compile at all with the different buttons
and menu entries (without errors). This has been described already by others.