Microsoft said in a support blog that it was working with AMD to resolve the issues and would resume Windows operating system software updates to affected AMD devices via its Windows Update process as soon as possible.

AMD shares dipped 1.3% in pre-market U.S. trading. Last week the stock rose nearly 20% as investors speculated AMD could wrest market share from Intel, whose chips are exposed to risks from possible Meltdown and Spectre attacks.

“To prevent AMD customers from getting into an unbootable state, Microsoft will temporarily pause sending the following Windows operating system updates to devices with impacted AMD processors at this time,” Microsoft said in its statement.

Microsoft (MSFT) said it had received complaints from AMD customers that their machines stopped loading the Start menu or taskbar after installing Windows operating system security updates.

Upon investigation, Microsoft said some AMD chipsets did not conform to technical documentation the chipmaker had provided, preventing Microsoft from successfully patching affected machines.

In its blog post, the software giant said the patches had caused computer screens to freeze up, or have so-called “blue screen errors” on Windows 10, Windows 8.1 and Windows 7.

Meltdown and Spectre are two memory corruption flaws which could allow hackers bypass operating systems and other security software to steal passwords or encryption keys, on most types of computers, phones and cloud-based servers.

AMD (AMD) said last week that differences in its chip designs from rival Intel (INTC) meant its products were at “zero risk” from Meltdown flaw but that one variant of the Spectre bug could be resolved by software updates from vendors such as Microsoft.

AMD was not immediately available for further comment.