Please ensure you have downloaded the correct ZIP file before attempting to install it. We have seen cases where the ZIP file is being renamed, either automatically or manually, during or after the download process.
The file you attempt to install into WordPress must be unmodified, must have a file extension of ZIP and whould not be extracted beforehand (unless you intend to use the alternative FTP method of installation).
This error, "PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature", is almost always related to the ZIP file having been renamed or modified in some manner.
It can also occur if your server is very low on disk space, so please check that.
Finally, feedback from WordPress.org suggests this could also be related to a glitch in the way WordPress handles multibyte encoding but that was supposed to have been corrected by WordPress v2.8
Here's an example of an error recently reported:
Installing Plugin from uploaded file: pushbuttonseo_com.txt
As you can see, the file being uploaded has a changed extension (.txt)
It's possible the fix could be as simple as changing the extension back to .zip, so give that a try.
It would appear there is a download utility (or a browser modification) out there that changes filenames on download. We haven't identified what that is, but regardless, once you have downloaded the ZIP file in preparation for upload to WordPress, please ensure the filename of the ZIP file has not been modified as in the above example.
Currently the ZIP file names are in the format:
Free (Lite): pushbuttonseo-lite.1.0.n.zip
Where "n" is the version number. Of course these are subject to change, but they will always be similar and will always have a file extension of .zip