Apologies if this is already reported / fixed, I did look but only found a reference to it having been reported but no fix.
The archiver can fail with newer versions of PHP due to a bug in curl see: https://bugs.php.net/bug.php?id=64177&edit=1
The problem is in the curl_multi_close() function but it only occurs if no handles were opened. Although not a bug in Piwik this is easy to work around and the fix makes the archiver a smidge more efficient too. Patch attached. All it does is to not call curl_multi_init() unless it is actually needed, therefore preventing the problematic calling of curl_multi_close() with no handles.
This bug stopped our archiver from running at all for two weeks and I'm sure we're not the only ones!
Attachment: patch to get around curl bug
In 2ffc22b: Fixes #3783 Thanks for the report & patch help