NumberField NotImplemented Error

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Hello!

I am currently trying to use NumberFields but I am getting random errors when using them. I am trying to construct a NumberField by using

K=NumberField(x^2 +x+ 1, 'y')

or

K.<y> = NumberField(x^2+x+1)

Sometimes it works out just fine and other times i just get this NotImplemented Error:

Traceback (most recent call last):
  File "/cocalc/lib/python2.7/site-packages/smc_sagews/sage_server.py", line 1234, in execute flags=compile_flags), namespace, locals)
  File "", line 1, in <module>
  File "sage/modules/free_module_element.pyx", line 2023, in sage.modules.free_module_element.FreeModuleElement.__pow__ (build/cythonized/sage/modules/free_module_element.c:14871)
    raise NotImplementedError
NotImplementedError

And after that I can't make it work anymore. I tried resetting variables but that doesn't seem to be the problem. Does anybody might have an idea what causes this issue?

Cheers