I am trying to merge many layers to one and the only working method I found is by copying features from one layer and paste in the desired layer. I tried to use MMQGIS - Merge tool but I get some geometry error (for e.g. polygon 2.5 ! = Unknown WKB 3003).
I tried with another plugin called multiplelayerselection but something strange happened: you can select all features from visible layers but it will only copy current layer.
What can I do to speed up the process? I have about 10000 layers, so doing one by one is very slow.