I just updated Unity, and reuploaded the HTML version of my game, but for some reason it keeps giving me this error:
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There was a problem loading your project:

No dimensions provided or detected

Please add viewport dimensions in embed options on your project's edit page
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I do not know how to set the dimensions, I'm just using the unity default set up, and the dimensions are set to 1500 x 900. It worked in the last build but as soon as I updated it it seems to have broken. 

As the warning message suggests, you can set the game size on your project's edit page, where it says "embed options" (between the upload button and the long description textbox). Unity is bad at telling the browser what the size should be.