'tf' stop to be recognised

I am a TA for a university class and today, the function 'tf' stopped being recognized on the school's computer during a class. It worked before. The function call works on other computers.

Any call of tf (such as 'tf(1)' or 'tf([1],[1 0 0])') causes:

Error using tf
  The class 'tf' contains a parse error, cannot be found on MATLAB's path, or is shadowed by another file with the same name.

'which tf' returns the correct path. I do not see any other file named tf.

'ver' shows that the control toolbox is installed.

Thanks,

[dpb]

Have you tried

1. clear tf
2. restart Matlab on the offending machine

Is this local or networked install?

[C.Blouin]

Thanks, I will try clear tf, although I tried to restart Matlab. It is a network install.

[dpb]

You can also without restart use

rehash toolbox
rehash toolboxreset

to force the toolbox path and also any aliasing functions to be refreshed.

doc rehash % for details