I'm assuming you're talking about spectre? If so, this is probably "rcut" as described in "spectre -h options". The default is infinity, except for bsource resistors. Given that you've not told us much about how this is affecting you, or what the model looks like, I suggest you contact customer support so you can provide some details (if you can't provide them here). There's not normally much benefit in having resistors larger than 1e12 because the default gmin is 1e12 too and so the chances of the resistance having any effect in the solution are pretty small.