Sudden error on MySQL IIS hosted website

I have a VPS with Windows 2008 R2 with IIS web server, MySQL database server. I have hosted around 100 of websites on this server. One of the hosted website is throwing following error message:

" mysql_connect() [function.mysql-connect]: Host 'MYSERVER' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts' in C:Domainsmydomain.comwwwrootincludeconfig.php on line 21 Could not be connect to mysql"

This website hosted before around 3 years. I have not made any changes in the code. But, all of a sudden, website has started throwing error message. After that, I have searched error logs and found following details:

ERROR: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'MYSERVER@123'') WHERE User=''root''' at line 1

I have restarted service as well as rebooted server. But, it has not resolved it.