Yep, when I did my beef tenderloin last week I had the same problem. Just would not seal properly. I ended up just hitting the seal button after about 4 failed attempts. It was evacuated enough that it stayed under the water line which I guess is all that counts in the end. It makes you want to leave about 6 inches of extra bag length just so you can keep it dry along the sealing end.
I Don't know if anyone else has this problem, but when I try to vacuum seal something, if there is any liquid, it wants to vacuum out and then not seal because the bag is wet. When I did the peas in cream I threw the open bag into the freezer for 20 minutes before vacuuming and sealing and it worked great. Should work for sealing things with a marinade also.
Mike