Indeed not a viewer bug. The script pre-processor simply reports that it cannot load an include asset/file:
Please, refer to the
pre-processor documentation (you will likely need to add a '#pragma include-from: some_folder' directive before the #include since, by default, the Cool VL Viewer attempts to include script assets from your inventory for LSL scripts, not files from your hard drive).
Also, I don't see how your script could compile properly at all with LL's viewers since those do not have a pre-processor...
Or it means that your script includes both the pre-processed sources and the (commented-out) non-preprocessed ones (but that the script provider failed to give you the include files sources with the script); in this case, switch to the "Saved script" tab (just after opening the original script) and copy all the sources with the exception of the commented-out un-processed code (starting with "//start_unprocessed_text" and ending with "//end_unprocessed_text" for Firestorm, or starting with "//********** Escaped, original, non-preprocessed sources **********//" for the Cool VL Viewer), and paste it back in place of the "Edited script" tab contents. Then you can save the script again.
I might add an "Edit raw script" button/action in the future so that you can choose skipping/cancelling the (automatic) un-preprocessing step, when you do not have access to the original #include files/assets...