This is something I get asked periodically, so it's worth adding here the explanation as to why some uploads fail even though they are slightly less than the 125kb file size limit.
The limit is 125kb but with files that are very close to that size you get a failure as the uploading process adds what's called overhead to the file.
Basically it means that, when the file is uploaded, it's split into small chunks called packets, and each packet then has a start and end point added to it, so the server knows how to reassemble all the bits into the correct layout at the other end, so your picture displays properly.
That overhead can make the file just slightly larger than the 125kb limit overall as the server limit works on the file size plus the added bits.
So if you have a file which is very close to 125kb (in fact I recommend this for any file over 110kb) make it very slightly smaller by compressing the image in your image software. It'll only need a very slight compression - e.g. on a 120kb file applying as little as 3% compression can reduce the file size enough to fit under the limit whilst not losing the image quality. Using Paint Shop Pro a 120kb file compressed by 3% comes out at 103kb, whilst 10% compression brings the size down to 47kb.
Most imaging software has an option to compress images in this way - although some may say compress by 10%, others may say reduce quality to 90% - both mean the same thing.