strange behavior of ex constructor from string

[Bernard Parisse]

> 
> That's probably because the zimmer7 file is syntactically incorrect,
> containing terms like
> 
>  20734047820658568988275936059402711947017728*^286
> 
> and
> 
>  604703470567171052x^32

Sorry! I didn't check for a correct syntax since every time I had something
incorrect, I got Abort. I will look more carefully in the futur...
Thank you very much!

Bernard