Not sure if this is useful information or not, but after 2 hours of frustration this could be helpful.
Tonight I cracked the laptop to get back on my (working) project and I got multiple errors that did not make sense. Every sketch I tried to compile, the IDE output the same errors on all.
Previous to compiling in Arduino IDE tonight, I had my sketch open in DEV C++ program to edit my code when I hit the "run" button by mistake which generated the same type errors before I recieved them in the Aruino IDE.
I uninstalled the arduino-1.0.5-r2-windows program and re installed it and continued to get these same errors. The errors below where generated by simply the following:
void setup () {
}
void loop () {
}
Errors:
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp: In function 'void setup()':
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:43: error: 'Serial2' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:44: error: 'Serial1' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:45: error: 'Serial' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:46: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:48: error: 'INPUT' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:48: error: 'pinMode' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp: In function 'void loop()':
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:96: error: 'uint16_t' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:96: error: expected `;' before 'throttle'
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:120: error: 'throttle' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:129: error: 'Serial2' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:140: error: 'digitalRead' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:142: error: 'HIGH' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:144: error: 'Serial' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:185: error: 'Serial1' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:192: error: 'Serial1' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:195: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:204: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:213: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:222: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:231: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:240: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:250: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:275: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:300: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:317: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:334: error: 'delay' was not declared in this scope
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\main.cpp:351: error: 'delay' was not declared in this scope
What I found was main.cpp in //hardware/Arduino/cores/arduino had been overwritten as my sketch. All attempts to restore folder failed. I copied main.cpp from restore folder and pasted it to//hardware/Arduino/cores/arduino to overwrite bad main.cpp file which seemed to copy, but reopening the main.cpp file would always open with my sketch.
I eventually had the mind to copy the code from main.cpp from a restore point arduino folder, paste it in DEV c++ and run. I just couldn't overwrite the main.cpp file otherwise. What I realized, I had pasted my sketch into an open main.cpp blank project in DEV c++ when it was run.
This fortunately worked and all is well again. Apologies if this is known to happen, I am not an expert.