How do I fix lighting on static mesh created from BSP?

How do I fix the unsightly lines that form when I create a static mesh from a set of BSP’s? The BSP’s (which looks fine) make the container on the left, but you can see what appears to be lighting errors on the Static Mesh on the right… These generally seem to persist even after the lighting is re-built for the level. Any help in fixing this would be greatly appreciated!