I found what the cause was:
0,15,30,45 * * * * php5 trajnet/wdl/wd-conditions-messenger.php5 2>&1 > /dev/null
I had to add the 5 to it. At 1and1, the default is php4.x. To use php5.x, one of the ways is to add the 5 after php on the file. I had it on the file, so I tried placing it before the path as well. That did the trick.
Regards,
Traj