This was reported on ask.sagemath.org: http://ask.sagemath.org/question/1244/symbolic-vector-norm
Here is an example
sage: matrix(SR,[[x]]).norm()
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
/Users/grout/<ipython console> in <module>()
/Users/grout/sage-trees/sage-5.0.beta6/local/lib/python2.7/site-packages/sage/matrix/matrix2.so in sage.matrix.matrix2.Matrix.norm (sage/matrix/matrix2.c:47759)()
/Users/grout/sage-trees/sage-5.0.beta6/local/lib/python2.7/site-packages/sage/matrix/matrix0.so in sage.matrix.matrix0.Matrix.change_ring (sage/matrix/matrix0.c:8151)()
/Users/grout/sage-trees/sage-5.0.beta6/local/lib/python2.7/site-packages/sage/matrix/matrix_space.pyc in __call__(self, entries, coerce, copy, rows)
554 return self(entries.matrix(), copy=False)
555
--> 556 return self.matrix(entries, copy=copy, coerce=coerce, rows=rows)
557
558 def change_ring(self, R):
/Users/grout/sage-trees/sage-5.0.beta6/local/lib/python2.7/site-packages/sage/matrix/matrix_space.pyc in matrix(self, x, coerce, copy, rows)
1403 x = new_x
1404 copy = False
-> 1405 return self.__matrix_class(self, entries=x, copy=copy, coerce=coerce)
1406
1407 def matrix_space(self, nrows=None, ncols=None, sparse=False):
/Users/grout/sage-trees/sage-5.0.beta6/local/lib/python2.7/site-packages/sage/matrix/matrix_double_dense.so in sage.matrix.matrix_double_dense.Matrix_double_dense.__init__ (sage/matrix/matrix_double_dense.c:3215)()
/Users/grout/sage-trees/sage-5.0.beta6/local/lib/python2.7/site-packages/sage/symbolic/expression.so in sage.symbolic.expression.Expression.__complex__ (sage/symbolic/expression.cpp:5926)()
TypeError: unable to simplify to complex approximation
The problem appears to be an automatic coercion to RDF or CDF. Maybe symbolic matrices should override the method.
Patch submitted. I also added an example to be sure, and corrected a little mistake in a test in sage/misc/functional.py