Watch out for all the blank lines and spaces Gaussian needs to work. I mean, ensure than your input looks like: (C means Charge, M means Multiplicity)

# keywords

(blank line)

Title

(blank line)

C1 (space) M1 (space) C2 (space) M2 (space) C3 (space) M3

Coordinates

(blank line)

Also check (just in case) that all charges and multiplicities are OK. The first ones (C1 and M1) are the charge and multiplicity of the whole system, whereas C2, M2, C3 and M3 are the charges and multiplicities of the system it is going to calculate at high level (the so-called model system).

Ensure that these latter charges are correct (the ONIOM model replaces atoms that belong to the low level for hydrogens in the high-low level bonds when it is calculating the model system)

Mrs/Miss Ingersol,

Remove geom=connectivity from the route section.

you write in route section these commends: nosymm and also geom=connectivity

i think that in this case it will be delete one of these commends:

nosymm

or:

geom= connectivity

Hallo, Laura!

Just small supplement to Enrique:

You demand all your (sub)systems to be neutral and in a singlet state. Your error message means that your (sub)system spin multiplicities do not agree with your (sub)system neutral charges. The most simple checking of this error message (in your case) is that every (sub)system must contain an even number (... 12, 14, 16 ...) of atoms with odd atomic numbers (H, N, P, F, Cl ...).

Best wishes

mb