16F628 acting funny...?

[Melanie]

If you have not assigned the MCLR pin to internal, example...

@ DEVICE pic16F628, MCLR_OFF ' Master Clear Options (Internal)

...then it has to be tied to Vdd or reset circuitry of some sort. Failure to do so will result in unreliable operation at best, or complete failure at worst.

[Bob_W]

And..... You are going to have more problems shortly. 4 AA batteries = something less than 6 volts into the regulator, which means that the regulator is just barely working - unless you've got a LDO (low drop out) regulator. Either add another AA cell so the input to the regulator is ~7.5 volts, or replace the regulator with a diode - 1N4148, etc. - to drop the 6 volts from the 4 AA cells to about 5.3 volts.