Nobody can tell you anything without proper system info or other technical details like actual render settings, version of AE and so on. That aside, odd formats simply may require to use specific CoDecs or image sequences all the way.
You cannot use mpeg codecs or standard video codecs for LED banners. You must follow the manufacturers recommendations for compression. Simple as that. You can render an image sequence or a Quyicktime any JPEG or PNG or TIFF movie, but those may not be compatible with the software used to run the banner so you HAVE TO ASK how they want the file. Never take a job without getting the delivery specifications in advance. Make that part of your contract and you'll look like a pro. Some LED signs require a proprietary codec that may not be compatible with your system.
Sorry I missed off more information. I'm using CC 2014 on OSX 10.9.5. The client has asked for MPEG-4 format, Overall bit rate 10000-30000 kps, Video format AVC, frame rate 29.970, colour space YUV, Chroma subsampling 4:2:0. Hope this extra information is useful.
AVC is h.264 and 4096 is the max recommended frame width for h.264 according to the spec and this is the widest format available in the AME.
So that means you'll need to find out from the client how they encode the video, render either an image sequence from AE or a Quicktime.Jpeg2000 or something similar, drop that in the encoder that they use and produce your deliverable product.