Did you change the filament diametre? This might cause your problem.
In general, there are several causes possible, it is probably the most common issue with 3d-printing.
It can depend on the printing speed (nearly as slow as possible), the surface (painters tape does a quite good job, but you need to re-level/calibrate then), the material, and, last but not least, the leveling (this is what Silhouette calls 'calibration').
A troubleshooting-guide in Spanish might help you as well, you need to read the section of print not sticking to bed. This is not Alta-specific, so you can use nearly every troubleshooting-guide.