How To Fix Layout BX Error

Hi There,

I have problems with the blogger layout function in the blogger dashboard : I can't change place of my widget with the usual "drag n' drop" method, a BX error message comes up every time and cannot saves changes anymore.
I have managed to change the layout using the "edit html" funtion, but it's not convinient.
Can this problem be solved by fixing the template editing the HTML, I'm guessing there must be errors in the coding but I'm a complete newby and don't really know what sort of errors I should be looking for.

Here is a little more info :

I've pusblished my first blog recently using a custom template (Minima Black 3 Col)
http://genuinevintagekicks.blogspot.com

I customized the template further notably widenning the main column and the two side columns, and then added several widgets such as a star rating widget.
After doing this the layout page shows a display bug that looks like this :



As you can see the right handside column is now displayed beneath the left one, I don't know why

Thanks for your help !

John