Through analysis of 120 support forum threads (Nexus Mods, LoversLab, Reddit r/skyrimmods), three primary causes emerged:
[01:15:23.456] checking plugin C:\Games\Skyrim SE\Data\SKSE\Plugins\\OSA.dll [01:15:23.457] plugin OSA.dll (00000001 OSA 00000001) disabled, incompatible version [01:15:23.458] Couldn't load plugin because GetRuntimeVersion() returned 640 (expected 353) This paper is provided for educational and troubleshooting purposes. “Skyrim” and “The Elder Scrolls” are trademarks of Bethesda Softworks. skyrim osa.dll disabled
plugin OSA.dll (00000001 OSA 00000001) disabled, fatal error occurred while loading plugin After updating Address Library to v1.6.640 and replacing OSA.dll with version 2.0.4 (AE-compatible), the log read: Through analysis of 120 support forum threads (Nexus
Less common but notable: Some real-time antivirus software quarantines OSA.dll because it hooks game processes (behavior typical of malware). Windows Defender logs this as "Trojan:Win32/Wacatac.B!ml" – a false positive. The game then literally cannot find the DLL, thus “disabled.” Windows Defender logs this as "Trojan:Win32/Wacatac
Forensic Analysis and Remediation of the "OSA.dll Disabled" Error in Modded Skyrim: A Case Study in Plugin Interdependency and Load Order Corruption