function.fopen]: failed to open stream

It turns out that ":" is reserved file name character in Windows. Please edit filecache.inc and replace return statement in line 56 with the the following simper return:

return urlencode($cid);

I hate hacking modules! Would it be possible to put in a test for Windows and perform the simple return, otherwise perform the original return. Something like:

    // see drupal.org/node/1153796
    // Don't do this for Windows.  The ':' character is invalid for a
    // Windows file name.
    if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
      return urlencode($cid);
    }
    else {
      return str_replace('%3A', ':', urlencode($cid));
    }

There may be a more elegant way of doing this, but this seems to work. I can now have this one version on my staging and production sites (Linux) and on my development site (Wampserver).

A proposed patch is attached.

Above works, but #1211166-7: Create separate directories for each cache bins fixes it too. By (a.o.) replacing all ':' by another character, on all platforms. (A space.)

Microsoft Windows is important platform that should be supported.

Fixed in c787423. I committed the solution provided by roderik to replace : with space and / with ^.