"Unusual Usage - Account Temporarily Locked Down"

Like many google user, I have this message popped out often than I can bear.
Operating system:. Win7 enterprise. 
Program and version you use to access Gmail Googlr Chrome developer mode and Internet Explorer 8  
Your antivirus software Maleware byte
Any extensions, toolbars or plug-ins: google reader, send this in gmail

Possible cause suggested by Google:

  1. Receiving, deleting, or downloading large amounts of mail via POP1 or IMAP2 in a short period of time. If you're getting the error message, 'Lockdown in Sector 4,' you should be able to access Gmail again after waiting 24 hours.(No mail client program like outlook or thunder ever installed before, so nothing involving POP IMAP should happened, since this error message come up often, Just wonder should I also get my gmail offline in case, or should I have another  webmail other than google, then forwarding my  message to there?)
  2. Sending a large number of undeliverable messages (messages that bounce back).(I do have undeliverable message, but not a large number, just one, and its been deleted)
  3. Using file-sharing or file-storage software, browser3 extensions, or third party software that automatically logs in to your account.(have not using file sharing/storage software on this account, another account that use storage function did not have this problem, I have google phone that automatically signed in, could it be? Some chrome extension, maybe: better gmail? One number?Super google reader?) 
  4. Leaving multiple instances of Gmail open.(Unless Google count my android phone's gmail as one instance of gmail open, otherwise no, by the way, how am I sure about android's gmail is off?) 
  5. Browser-related issues. Please note that if you find your browser continually reloading while attempting to access your Inbox, it's probably a browser issue, and it may be necessary to clear your browser's cache4 and cookies.(Just checking if gmail back  to normal, and I got the following error message:  We're sorry. It seems there is a problem. Please try using Gmail with a supported browser. If you're encountering this error while using a supported browser, we suggest alerting your Internet Service Provider (ISP) that a proxy is failing to accept cookies on HTTP redirects.
Click here to return to Gmail. You'll need to sign in to your account again.(
Possible cause

  1. My associated google android phone
  2. facebook connection
  3. possible blockout for fearing China hacker attack.
  4.  
Possible work around solution:
  1.  it works fine through igoogle.com and via my IMAP connection in Outlook.
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