opening sopc system (9.1) with version 10

I'm not sure whether or not this applies in your case.

I had a similar problem with our previous design in SoPC 9.1 sp2 (including nios, ddr2 and some vip and custom ip for SIII). The design had errors upon opening in Quartus 10.

in our case, it turns out the source of errors were libraries, becase we didn't installed all of devices ( I only installed Stratix III and Cyclone III ) the SoPC builder couldn't compile the sopc. the errors were fixed upon re-installing quartus with ALL devices support.

P.S. For us, the particular error source was VIP CTI and ITC ips. They required stratix II device libraries to work on stratix III fpgas.