In addition to the great advice by David, you should also consider that connecting any test instrument will alter the signal you are testing. This
observer effect is unavoidable.
So consider carefully how your voltage probe is affecting the current through the resistor. A basic "10 MOhm" passive probe has about 15 pF of tip capacitance. At 40 MHz (which is what I assume you meant), the reactance of that capacitance is about 250 Ohm, and this is in parallel with your 50 Ohm resistor, so some current will be shunted through it. Also consider that the current probe is actually a transformer, and by clipping this onto the resistor, you have effectively added a series inductance to the resistor, which increases its impedance. So you should expect the current to be lower than expected, if that makes sense.
Also keep in mind the frequency response of the probe. It isn't a perfect flat line to its rated 60 MHz. At 60 MHz, it should be about 3 dB down (about 30% low), and at 40 MHz it will definitely be down a bit already.