[Zope] zsql methods in zclasses give authentication errors

[chas]

Is there any reason why ZSQL methods which work fine within 
folders do not work within Zclasses ? Instead they seem to 
give authentication errors.

eg. 

/Products
	/Myproduct
		/MyClass
			/Methods
				/index_html
				/dtml_method
				/sql_method


The ZSQL method works correctly when I try "test" - which 
means that the DB connection and SQL are correct.
The DTML method ('dtml_method') calls 'sql_method' and parses
the output.  However, if I create an instance of this
product and then try to access dtml_method using 
http://Zope/Instance_of_Myproduct/dtml_method
I get a "authentication failure" and a pop-up asks me to 
log in again; however, not even Zope superuser can log in !

Before, I had these very same methods in a folder :
/Folder
	/dtml_method
	/sql_method
and it worked perfectly. 

I've enabled *every* permission in the zclass to allow full
access but still this authentication error. Has anybody else
encountered this ?

Apologies for yet another post/question but :
a) I've looked/searched the archive and tried almost everything.
b) After previous experience with zclass, I don't want to waste
   too much time if it's actually a problem with zclasses.

So, any help greatly appreciated. cheers,

chas

ps. running zope 2.0 on NT