I am a novice user of 6 weeks.
I backed up my site then upgraded to WP 3.5 last night.
This morning there were 3 Plugins that required an update but when I tried to upgrade I received this error:
PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature.
Checking old support threads suggested that it might be I was at the limit of my hosting amount or file permission errors.
It is not hosting limits and Hostgator have checked my file permissions.
Updating plugins was fine yesterday BEFORE upgrading to 3.5.