Madrid - A fraud investigation of Spain's Princess Cristina was thrown into disarray on Tuesday when the Tax Agency said it had been mistaken in reporting she had been the seller of 1.4 million euros (S$2.4 million, US$1.87 million) worth of properties.

Cristina, daughter of King Juan Carlos, is under investigation for alleged tax fraud as part of a wider corruption probe against her husband, Inaki Urdangarin, who is charged with embezzling 6 million euros of public funds.

Spaniards hit by 27 per cent unemployment have soured on the once-popular royal family as the Urdangarin scandal drags on.

Last week the tax office handed the court a report showing that the Princess had sold properties worth 1.4 million euros in 2005 and 2006, including a house in Barcelona and rural plots.

The Princess's lawyers denied she had ever owned any of the real estate in the report.

Owners of the properties in question also told local media they had purchased them from people known to them, and not the Princess. The titles on four small farms, for example, were transferred between members of a family on the date that the Tax Agency had reported they were sold by the Princess.

On Tuesday the Tax Agency said the report contained errors.

And the government property registrar office clarified that the Princess was never the registered owner of any of them.

"The report of property deals by Doña Cristina de Borbon y Grecia was in error due to the fact that the Agency received information involved a National Identity Document with the same number as hers," the Tax Agency said in a statement.

Spain's royals have two-digit national identity numbers - Princess Cristina's is 14 - while commoners have eight-digit ID numbers. The Tax Agency did not clarify how its experts confused such different numbers.

The agency also did not explain how the same error had occurred in several different provinces.

Examining Magistrate Jose Castro called for an investigation into how the erroneous report had come about and Spain's most influential newspaper, El Pais, in an editorial on Tuesday in its on-line edition called for a full government explanation of the mess-up.