You should save your sketch with a meaningful name
How would you ever determine in two weeks what the file "sketch_dec11a" does??
For the error-message
The Arduino-IDE can be configured to log only a few = too few things about the compiling-process and errors or very much details
So as the next step you should adjust the arduino-IDE to printout each and every detail about the compiling process like described in this tutorial
best regards Stefan