unable to log in ubuntu :(

Hi
I m not able to log into my ubuntu account whenever i try to login ubuntu gives the following error:

GDM. could not write to your authorization file.this could mean that you r out of disk space or that your home directory could not be opened for writing.
in any case ,it is not possible to login.plz contact your system admin

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this happend when i transfered lot of data in my small ubuntu partition

writting this post from my friends P.C

plz help me fast what can i do ? I can only go to ubuntu recovery mode but no GuI from there