There seems to be about a 128 KB limit on the size of files that can be attached to posts. This is a small limit, smaller than it used to be.
When trying to attach a file larger than 128 KB, it seems to upload but then the status indicator shows an error ( ), clicking on it gives a popup message
"ERROR Failed to move uploaded file."
Looking at the page source, I see the javascript is defining two variables
max_file_size: '262144b',
chunk_size: '131072b',
it seems to be limiting it to the chunk size, whatever a chunk is in this case
I don''t know what file size you want the limit to be, but the feedback to the user isn't helpful, took me a while to figure out why I couldn't upload a 135KB gif The attachment size limit used to be about 1MB, the javascript seems to indicated a limit of 256 KB, and the current reality is about 128 KB