Bizarre, as I haven't shifted my test network to 1.5.15 I can't emulate the precise environment but as a guess it could be related to the limits on POST or even modsecurity2. The module code isn't really used at in the module manager of Joomla - it just parses the mod_miniadspot.xml file which can contain any old rubbish. So my guess is some unique combination of thing is broken on your site. What I would aim to look at is to use Wireshark (www.wireshark.org/ it's OpenSource free and awesome) and with this you can trace what your browser sends and the actual web server response. From this it should be a bit clearer. The POST is quite large and perhaps the web server is choking on this. A way to test this would be to edit the mod_miniadspot.xml and remove loads of those <param> </param> sections for the ad spots so that you only have a few spots listed. Then if that cut-down version saves then the problem is your web server is limiting POST sizes.

That was the solution.

I deleted <param name="priority4 / <param name="priority 20 and changes de name miniAdspot. Then uploaded the zip to Joomla and that worked. Now I can change the name trough joomla.

Thanks

That's not really a solution as you have taken out many of the entries for Miniadspot !. Using Wireshark on my system I see a POST of 5271 bytes (5 TCP segments) and then a response from the server of 301 Permanently moved (pointing at Location: <my server>/administrator/index.php?option=com_modules&client=0rn).
I wouldn't imagine that your POST can be any bigger and this is well within the usual megabyte size limits. Something has to be setup different with your server. Did you try Wireshark too ?