String keeps snapping/slipping out of floating clamps.

Purchased a Pro Stringer (portable one).

I've never used floating clamps before, as 90% of the racquets I've strung were on a Babs Star 5. Right now everytime I lock the floating clamp on the two middle, then go to the next hole and pull tension to start the mains the string snaps or slips out of the floating clamp everytime. Beyond frustrating now. Am I doing something incorrect? Went on YouTube and watched the vids and am doing exactly what these guys are doing. It is rough poly (Babolat RPM). But still.
Hi MastureB, I agree that the stock clamps are not really up to the task. I'm now using Stringway Flying clamps with mine and have absolutly no problems at all.

I used the following proceedure to fix the supplied clamps on my Pro Stringer and the slipping issue was largely resolved. Ultimately a set of Stringway clamps are the way to go though.

You will need:
2 3/32 allen keys
1 large Philips head screw driver
Some 80 grit wet and dry sand paper

Step 1. Disassemble the clamp by removing the two counter sunk Allen head bolts with the Allen keys.
Step 2. Remove the tensioning bolt with the Philips head screwdriver, the metal side plates will now come off the clamp body.
Step 3. Using the 80 grit sand paper scuff the inner surface of each metal side plate where it makes contact with the string.
Step 4. Wipe the side plates clean and reassemble the clamp using the reverse of the above steps.

I was having lots of problems stringing Multi filament string (Solinco Vanquish 17G) when starting the mains.
After doing the above proceedure, I’ve tested my clamps using Vanquish 17G tensioned up to 65lbs and they are now holding securely.