Saving selection as new shapefile using QGIS gives OGR error?

I have an issue saving a set of polygons as a new layer that I've selected using the polygon select tool in QGIS.

After selecting the polygons in the main (source) layer, I've tried two ways:

1. I tried Edit> copy features > paste features as new vector layer. After which I get the dialog box below. A also tried paste features as new memory vector layer - which created a layer, but there were no attributes in the table - is was empty

2. I tried another way of right clicking the selected layer > save as > save as > and clicked the 'save selection only' in the 'save vector layer as...' dialog box. I got the same dialog box.

Any ideas welcome.