How have courts dealt with the collection of taxes on property exempt from taxation?

The collection of taxes on property exempt from taxation is an erroneous or illegal collection within the meaning of section 5096, Revenue and Taxation Code. (City of Long Beach v. Board of Supervisors, 50 Cal.2d 674, 679, 328 P.2d 964.)

Another instance of erroneous or illegal collection is where the tax rate has been fixed upon an assessed valuation that excludes from the levy a material portion of the property on the tax rolls. (Otis v. Los Angeles County, 9 Cal.2d 366, 377, 70 P.2d 633.)