Can't drag sprites into the sprite collection editor.

[mr.FamousOne]

Hi guys,
I have downloaded the city-building-kit along with its dependencies, of which TK2D happendes to be one.
While trying to replace the tiles in the package with my own, I followed the documentation and tutorials and did the same.
At first when I opened the 'sprite collection editor' after creating and renaming a new sprite collector. It all seemed to work.
I then dragged the sprite into the editor and it went but then Unity stopped responding and i had to close Unity.
I then reopened the project and tried again to load the sprites into the collection editor but nothing is happening.
The editor would not allow me to drop any sort of sprite into it at all. Even where it dictates that i should. However when I use the create->sprite sheet button. I am allowed  to drag and drop into the 'sprite sheet texture' window.
I have spent hours and hours trying to solve this glich but to no avail.
I have contacted the city-building-kit guys and they have tried to sort it out for me but still i have not succeeded.
I even totally uninstalled and reinstalled Unity and the packages. This did not work either.
Can it be something i am doing wrong?
Could it be a glich somewhere?
I have attached the screen shots of the collection editor.
please help me out here.
thank you.
Mr.FamousOne