When I'm trying to run a map on geomajas an error has occurred:
o.g.internal.service.GeoServiceImpl - Problem during transformation EPSG:4326->EPSG:900913 of MULTIPOLYGON
The multipolygon coordinates are x = -170 and y = -85.0511... .
Your problem is with the bounds of EPSG:3857, the "WGS84 Pseudo-Mercator" projection. It has latitude limits of +/- 85 degrees. So your point of -85.05... is outside the bounds, and is undefined/untransformable. You'll need to use a projection that covers greater latitudes, and the choice of that will be very much based on the extents of your data, the levels of accuracy which you're willing to accept, whether there is going to be other layers from other projections, and so on.
In Geomajas, you can define the transformable area for pairs of projections. See http://files.geomajas.org/maven/trunk/geomajas/docbook-devuserguide/html/master.html#ch-crs When a transformable area is defined, geometries are clipped to fall inside this area. This should solve the transformation problem for you.
In any case, you should post the full stack trace of the exception (maybe on something like pastebin and linking that here). This can give useful hints for solving the problem.