Might help if you explained what tool you're using to do the simulation, or where you placed these save statements. If they're in a spectre netlist, you'd have to use the spectre namespace - so you'd probably put:

save I0.xxxa I0.xxxb

If in ADE, you could use a stimulus file and then use the syntax for mapping the Virtuoso namespace into the netlisted namespace by using:

save [#/I0/xxxa] [#/I0/xxxb]

This is assuming that the referenced blocks have been netlisted by ADE, and it will take into account any mapping that has been performed on the names of those nets.

I'm having to guess here, because you gave very little information.

Regards,

Andrew.