I am using the open source version of qcad, and while it says on
http://www.qcad.org/en/qcad-documentation/qcad-features that layers are supported in this version, the software requires the pro plug-in to be available.
Layer support
Moderator: andrew
Layer support
From a QCAD user:
Re: Layer support
Please uninstall the trial versions of the Pro plugins as described on the download page. Then restart QCAD.