I have an issue with digitizing lines in QGIS 2.18.2. I was using cadtools and after digitizing lines in my Lines layer on saving i get the message:
--Could not commit changes to layer (insert layer name)
Errors: ERROR: 1 feature(s) not added - geometry type is not compatible with the current layer.--
I have digitized a line in a line layer - that is certain.
I have tested without using the Cadtools and it appears that even if i use the snapping tool to digitize to a feature it throws the above error but if i just digitize a random line not using snapping then it is able to save.