using Hardware serial and interrupt together

Hi Everyone
i am trying to use Hardwareserial communication and external interrupt at the same time
whenever i am trying to do this i am losing data i am using pre designed wifi chip it sends serial data continuously to the mc. When ever the interrupt is activated the serial communication no longer works so is there any way where i can make both of them work.
Note:As soon as the board is powered on the interrupts are activated.
A zero crossing detector 4n35 is used to produce the interrupt
Serial communication also works continuously

i am using arduino uno board

Without seeing your program how can anyone offer any suggestions?

...R

In addition to R2's request a schematic may also prove useful.

Bob.