QM/MM error

[jacopos]

Dear all
I'm trying, for the first time, to run a QM/MM  simulation on a
protein.
I checked accurately my input, but I'm not still able to solve this
error:

*** Detected a non contiguous molecule!! Too late at this stage  ***
 *** everything should be already ordered! Try with the keyword   ***
 *** reordering.. It may help!

I'm using an Amber topology and coordinates from a pdb file.
I've also used the REORDER keyword but it does not work.

Does Anybody have experience with this error?

Thanks in advance