Re: Protel error message
The error you are seeing is most often caused by using a comma (,) as a separator in numerical values. Some languages use a comma as a decimal separator, but Protel expects to see a period (.).
If you are using AD2004, set the regional settings to an English based setting. That will make the decimal separator a period.
If you are using DXP, Open the Regional and Language Options. From the Regional Options tab, select the customize button. Make sure all decimal separators are set to the period, then apply these settings. You don't need to resart the program for the change to be effective.
The answer to your other question is that a "mixed" layer uses polygons on a signal layer for plane connections. A "cam" layer is a true plane. If you do as I suggested above, you can use the normal plane layers, as well as signal layers.