When I try to use Dissolve in Processing I get this error:
"local variable 'nElement' referenced before assignment See log for more details"
I have seen this problem reported in: https://hub.qgis.org/issues/14612
So then I did what is recommended by Alexander Bruy removed the processing folder from C:\Users\user.qgis2 however I still have the same problem, I did a Full Uninstall (delet all folders…) of Qgis and reinstalled from standalone installer QGIS-OSGeo4W-2.14.3-1-Setup-x86_64 but the problem persist.
I suspect that it is a bug…
PS: when I use the "Dissolve all" check, the process work, its only when I try to dissolve from a selected field that give me the error
QGIS 2.14.3
Windows 10 64bits (1511 10586.318)
Processing 2.12.99
Best Answer
You can use Vector polygon tools > Polygon dissolve (by attribute) from SAGA in the Processing Toolbox. I had the same issue.