I haven't seen that message, but here's some background/explanation:
Many consumer internet routers include a (essentially useless) feature called "SIP Application Layer Gateway", or ALG. There's no good reason to have it enabled, and it can interfere with two-way audio during SIP calls. OBi may have some sort of test that attempts to identify that condition, and it can't tell what the state of the setting is, in your case.
As long as you don't have any problems with either party hearing the other, then no worries. If you are curious, you can plow through your router's settings to see if it shows a setting for ALG, and if it does, then disable it.