Have had this error now for last two versions (1.06 and 1.07) after an initial successful use on 1.05.
Advanced IMAP is enabled (and works for Offline when enabled!) but currently Backup won't even start.

I started off recommending this program to Gmail users, but now find myself unable to use it. :-(
~~~~~~~~~~~
Error: Error occured, full traceback is bellow (gmb.py revision 691)
Traceback (most recent call last):
File "gmail-backup-gui.py", line 109, in _runThread
File "gmb.pyo", line 1218, in backup
File "gmb.pyo", line 630, in connect
File "gmb.pyo", line 617, in guessLanguage
ValueError: Cannot access IMAP folders


Traceback (most recent call last):
File "gmail-backup-gui.py", line 109, in _runThread
File "gmb.pyo", line 1218, in backup
File "gmb.pyo", line 630, in connect
File "gmb.pyo", line 617, in guessLanguage
ValueError: Cannot access IMAP folders


Just downloaded the latest version.
Every thing works just fine. I get all mails in my Outlook, an ofcourse in the webmail.
Outlook connects through IMAP, so I don't see this as the issue.

Any Ideas?

Btw. I'm using the app on a google apps account

I had the same error and JohnW's solution works fine !

Only put "show on imap" to "all mail" label on gmail set up and works fine !

Thankkkk u !!!!

Hi JohnW
I followed your way but can not resolve this. I try to do it several times but it still have the problem. How can I solve it, every ones?

GMail Backup revision 691 (2009-02-20)
Starting backup of account tuantab@gmail.com into E:\Tuan's Document\Gmail-tuantel backup 22-Jun-11
Error: Your Gmail account doesn't export some IMAP needed to Gmail Backup work.
Possible causes are:
- You are using the Gmail Labs.
Please go to the Settings/Label page and enable the IMAP access into
All Mails and Trash folders.
- You are using unsupported language of Gmail. Please run the following
command:

gmail-backup.exe list

and send the output of this command at info@gmail-backup.com.
Thank you
Error: Error occured, full traceback is bellow (gmb.py revision 691)
Traceback (most recent call last):
File "gmail-backup-gui.py", line 109, in _runThread
File "gmb.pyo", line 1218, in backup
File "gmb.pyo", line 630, in connect
File "gmb.pyo", line 617, in guessLanguage
ValueError: Cannot access IMAP folders

GMail Backup revision 691 (2009-02-20)
Starting backup of account tuantab@gmail.com into E:\Tuan's Document\Gmail-tuantel backup 22-Jun-11
Error: Your Gmail account doesn't export some IMAP needed to Gmail Backup work.
Possible causes are:
- You are using the Gmail Labs.
Please go to the Settings/Label page and enable the IMAP access into
All Mails and Trash folders.
- You are using unsupported language of Gmail. Please run the following
command:

gmail-backup.exe list

and send the output of this command at info@gmail-backup.com.
Thank you
Error: Error occured, full traceback is bellow (gmb.py revision 691)
Traceback (most recent call last):
File "gmail-backup-gui.py", line 109, in _runThread
File "gmb.pyo", line 1218, in backup
File "gmb.pyo", line 630, in connect
File "gmb.pyo", line 617, in guessLanguage
ValueError: Cannot access IMAP folders

You are using the latest version of GMail Backup.
GMail Backup revision 691 (2009-02-20)
Starting backup of account tuantab@gmail.com into E:\Tuan's Document\Gmail-tuantel backup 22-Jun-11
Error: Your Gmail account doesn't export some IMAP needed to Gmail Backup work.
Possible causes are:
- You are using the Gmail Labs.
Please go to the Settings/Label page and enable the IMAP access into
All Mails and Trash folders.
- You are using unsupported language of Gmail. Please run the following
command:

gmail-backup.exe list

and send the output of this command at info@gmail-backup.com.
Thank you
Error: Error occured, full traceback is bellow (gmb.py revision 691)
Traceback (most recent call last):
File "gmail-backup-gui.py", line 109, in _runThread
File "gmb.pyo", line 1218, in backup
File "gmb.pyo", line 630, in connect
File "gmb.pyo", line 617, in guessLanguage
ValueError: Cannot access IMAP folders

Cannot access IMAP folders 에러 해결방법입니다.
한글이 없어서 한글로 씁니다.

Gmail 환경설정에서 IMAP 보여주기 체크 해제된것
모두 보이기로 체그하면 백업됩니다.

몇몇분들은 스마트폰등에서 간단히 보기위해 IMAP 보이지 않기 체크를 해놓으셨을텐데 보이기로 체크하면 보입니다.

이글 보시는분들 성공하시길...

Just select imap in labels for all folders and then it works like a charm