Hi, i've the same issue, but there is the workaround:
the system says "Error in application /" etc. etc... every time that you send some data, but behind the scenes the data are stored. The problem is that the error page doesn't allow you to continue your submission, so for that the solution is the little menu in the left: you have to select sequentially the various steps, compile every form and send the data, then go back in your browser, select the next passage from the menu and send data. At the end, select the PUBLISH option and your game will be correctly (more or less) send to Scirra Arcade!
Here my last game, i've found this trick trying to upload it:
scirra.com/arcade/action-games/qbos-adventures-33770
Maybe this can be useful to everyone that have the same issue (i've read a lot of posts about this...) Tom ?