PC to EUART on pic 16F688

[skimask]

I'm using the internal oscillator at 4MHz and running at 2400 baud.

That's most likely your problem right there. Go with external crystal, resonator, oscillator, something...
But since you said you're having overrun errors, look at the 'F688 datasheet in the OSCTUN section and dial down your internal clock a couple of notches and see what happens.
Problem is, this will only work at that particular battery voltage, that temperature, that day of the week, when the moon is in that particular phase, etc.etc.etc...
Just save the trouble and go with an external clock source...
Could it be something else causing the problem?
Sure...trying to SEROUT while at the same time receiving serial data in the hardware...bad idea... I'd also be willing to bet if you took all of those SEROUT statement and made it so that each SEROUT statement only did one, two, maybe three characters at a time, you're overrun errors might go away, since it'll give the program/hardware a chance to interrupt and empty out the incoming hardware serial buffer.

[Emil G]

"SPBRG = 25 ' Set baud rate to 2400 for USART" ????

SPBRG = 25 ' Set baud rate to 9600 for USART !!!!!

[Archangel]

"SPBRG = 25 ' Set baud rate to 2400 for USART" ????

SPBRG = 25 ' Set baud rate to 9600 for USART !!!!!

???? SPBRG = 25 is 9600 at 16 mhz it is 2400 at 4mhz