Is this a normal FlexCel installation, or have you installed it manually? If installed manually, please make sure that FlexCel .pas files are not in the library path. (only dcus should be there). Normally this error is because Delphi is trying to recompile FlexCel, and crashes with some generics. But this shouldn't happen if FlexCel isn't recompiled.
If this is with a standard FlexCel installation, does it happen with an empty project? Or only with specific stuff? Can you compile the android demos?
Even when I hadn't personally seen this befor, it seems to be a generic delphi error not specifically related to FlexCel. I wonder if you can try the things suggested in this thread:
Also, if it works in Release, then the cause might be that the debug information for FlexCel is getting too big. Other thing to try would be to uncheck "Use Debug .dcus" in your project options. (Delphi Compiler->Compiling). This will remove the ability to step in FlexCel sources when pressing F7, but it should reduce the size of the exe a lot, and still allow you to step and debug your code.