The link you provided is working fine - can get an xml result back from that without any problem.

Turning on debug mode for the ozpost module, and telling the module to spit out the value of $qu before it hits line 345, it seems to me that not returning data in xml format? under some conditions which is then throwing line 345 which tries to process the xml...?

Not sure what triggers it to work/not work as have another site on the same server that is working absolutely fine without any problem....? Can't find any material differences between those two sites at all.

Putting in the code die ($qu);exit after the $this->_getAPdata line in the offending module, returns

324 PPS39.94 3Kg Prepaid SatchelPPSE311.31 3kg Prepaid Satchel ExpressRPP11.6 4 Regular ParcelREG14.45Registered ParcelEXP17.3 1 Express ParcelCOD21.85Cash On Delivery 0 2.8 0

shouldn't this be xml? or did I do something wrong.

I'll sit on it until tomorrow to see if further propagation fixes it, but just wanted to raise this as a potential problem in case it raises any flags for you and is indeed a bug. hope this helps.

fingers crossed.