Overflowed buffer

Hi,
I modified "plain.c" to add another parameter as an image to the sasl
server. Now the parameter structure would be as below:

*Authentication-id Authorization-id Password Image

The fourth parameter Image will be a base-64 converted string. When I tried
passing a image of small length say (20000 characters), There is no problem
in it, The mechanism can accept it. I tested the same with huge image where
the base-64 string is of (1,00000) characters. I am getting the response
"Overflowed Buffer".

What Will be the issue here? I am calling the SASL mechanism from client
end via IMAP.
*