One of the most common difficulties people run into when using EpicTable is selecting very large images for maps or tokens or portraits. The symptom of this is an image that fails to load for one or more participants in a game. Fortunately, the solution is pretty simple: watch your image sizes.
I'll often see someone using a huge image (let's say 1000x1000 pixels or something) for a token or portrait. The problem with that is that you're never going to use all that, and yet you're paying for it in memory and network bandwidth. Most portraits are shown at 300x300 and tokens are typically even smaller--50x50 by default for a medium creature, maybe as much as 400x400 for a dragon. The math here isn't linear, so that 1000x1000 image isn't just 3x larger than your 300x300 portrait. It's close to 10x larger. It gets worse. If you use a 600 dpi image meant for printing or from a scanner, you end up with an image way larger than necessary for your screen, which is 96 dpi by default (or 150 dpi on some big screens). For best results, limit image sizes to 300x300 or less and 96-150 dpi for portraits and tokens.
Maps have the same considerations. Sometimes people use maps meant to be printed. I've seen people try to use 6000x6000 pixel maps at print resolution (600 dpi). That's sure to cause memory and network problems. Very often people do this out of a desire to have one huge map for an entire adventure. A better way to think about using maps is as battlemats for a specific encounter. I create one map per encounter, using an image editor to chunk up larger maps if need be. What you're shooting for, in terms of map size is no larger than 2000x2000 and 96-150 dpi.
So, the moral of the story: limit your image sizes for portraits, tokens, maps, and other things. You'll consume less memory and experience less issues with loading images across the network.