If you are using the ISOLATOR output connections from the device then your signals are likely being converted to DC RS232 signals (and inverted) rather then being normal bipolar RS232 signals. Note that the ISOLATOR side also needs power and gnd inputs and likely a pull up resistor above the transistor collector.
So basically if that is the arrangement you have the voltages from/to your device are not compatible with the voltages from/to your PC.
If you connect the ISOLATOR collector pins to a pull up resistor at +5, and the emitters pins to gnd you can use a chip like a MAX232 to convert the collector signals back into the required voltages that match the requirement of the PC.
I was not able to access the tinyupload.
Did you add the power, gnd, and resistor parts as above? Are you using another chip like a MAX232 to reconvert the DC signals to be PC compatible?
If you still need to add the conversion circuit between the ISOLATOR side and the PC you may need to implement something similar to one of these:
You didn't mention if you needed to send data from the PC back to the device. If not then you may only need part of the circuit linked above.