Applies to: WebFront 4
Even if you increased Maximum size settings for work items and WebFront allows you to select larger files than default size, files aren't attached when you click OK/Apply. If you check browsers developer console you will see the "500 (Internal Server Error)..." error message.
By default, IIS Max Request Length is set to 4096 KB which will prevent larger files than that to be uploaded in WebFront even if SCSM settings are configured for a larger size.
Follow the instructions in the article Configure IIS to allow upload Attached Files > 4MB to increase the max request length size.