I would check for anything that's open for edit, or missing dependencies. If they're open for edit select them, right-click and revert to original. Missing dependencies are bit more annoying. Right-click and choose download. If the asset is on the DLS, then the parts should download too. There's been some issues where dependencies don't arrive on the DLS at the same time causing missing dependencies.
You may also want to check for updates. If you have any DLC, update that via the Content Store. You may also need to download some updated components through Content Manager. Everything but the routes and locomotives in DLC appear to be updateable from downloads on the DLS. You need to right-click on the DLC packages in Content Manager and choose show asset-versions. This will open a new window from where you can download the updates.