python XML element removal error

I read an tree from a file as a string and remove from it namespaces.

with open(pathArxmlFileName, 'r') as myfile:
    data=myfile.read();
data = re.sub(' xmlns="[^"]+"', '', data, count=1)
self.root = ET.fromstring(data);        
self.tree =  ET.ElementTree(self.root)

I want to remove an XML elemet from this tree

I tried:

for EL in self.root.iter('tagString'):
    self.root.remove(EL);

This find EL elements but when I call remove() function gives error:

   self._children.remove(element)
ValueError: list.remove(x): x not in list

Please help me , i dont know what to do :(

Ps:Modification of the tree by modifying an element value works