CrossRoads:
This part?
http://www.ti.com/lit/ds/symlink/cd4040b.pdf
It cannot drive a 50 ohm resistor, that would take 100mA at 5V.
See page 3 - It's only capable of 0.4mA of drive current with Vcc at 5V.
You can put a MOSFET in the circuit as a current driver.
Or a part like ULN2803 if you need to drive more optocouplers.
In all likelihood he just needs to use a larger resistor. Optocouplers, do not require much current to operate properly. 0.4ma should work fine. If not choose a different optocoupler. They were originally used with TTL/CMOS parts that could supply far less current than the modern microcontrollers.