The reason for the error is because they are trying to set the size of a variable that is not created if the script doesn't reach a specific point.
Albeit good practise to do so it is not required to set the size of the databloc's to 0 after you are finished using them. The Javascript Garbage collector will do this automatically.
Therefore all of this is unneccessary:
js code:
hMixerBloc.Size = 0;
mxl.Size = 0;
mxl2.Size = 0;
mxcd.Size = 0;
mxcd2.Size = 0;
mxc.Size = 0;
mxlc.Size = 0;
pmxcdSelectText.Size = 0;
pmxcdSelectText2.Size = 0;
/ 
