The remote normally is delivered by Comcast with the Cable setup code locked. You can check that by watching the LED.
1) Tap the Cable device button.
2) Hold Setup until 2 blinks
3) Enter 01877 (SA 8300 uses this setup code)
The remote should blink twice. If it doesn't, and instead gives one long flash. then probably the setup code is locked. Unlock it by:
Tap the cable device button
1) Hold setup until 2 blinks
2) Enter 982
The remote should blink 4 times. If it blinks 2 times, do steps 1 and 2 again.

Now try assigning 01877 again.

Oh, and is the OK/Select button red? If it is grey, then the setup code should be 4 digits-- 1877.