Chinese authorities have issued a 20-day deadline for Microsoft to explain “compatibility problems” with its Windows and Office software, after previously warning the company not to obstruct an anti-monopoly investigation. China’s State Administration for Industry and Commerce (SAIC) posted an online notice Monday demanding that Microsoft offer a written explanation within the allotted time. The antitrust regulator has been investigating the company on industry complaints that Microsoft software has “not been fully open,” resulting in compatibility and bundling issues with the products.