Hello maribel,

When you hitting this error message is because you haven't compile the stylesheet yet, can you try the following instruction and see how it goes?

Joomla backend > Easydiscuss > setting > Layout > General > select Compile stylesheet to "Cache" > Click "test compile" (test admin, site, and module) > when all test completed > then go to Easydiscuss Dashboard > Click "Clear Cache" > Then clear Joomla cache.