Windows/Excel更新后，.NET6+C#开发的Excel-DNA项目出现Excel-Dna.xll找不到及无法访问xyz.xll的问题

Hey there, sorry to hear your Excel-DNA add-in stopped working post-update—total bummer when system updates break perfectly functional tools! Let’s tackle those two error messages one by one with actionable fixes:

Error 1: "Excel 无法找到 Excel-Dna.xll" #

This usually boils down to path issues, permission resets, or trust settings getting wiped during updates:

• Check folder permissions: Windows updates sometimes reset permissions for protected directories (like Program Files). Move your Excel-DNA project’s output folder to a non-restricted location (e.g., Documents/MyExcelAddins), or right-click the existing folder → Properties → Security → Edit → add your user account and grant Full Control permissions.
• Update Excel’s trusted locations: Updates often reset Excel’s trust settings. Open Excel → File → Options → Trust Center → Trust Center Settings → Trusted Locations → add the folder containing Excel-Dna.xll and check "Subfolders of this location are also trusted".
• Verify xll path references: If your project uses relative paths for Excel-Dna.xll, the update might have broken the path association. Open your .xdna file or project settings, confirm the path to Excel-Dna.xll is correct (use an absolute path if needed), then clean and rebuild the project to regenerate output files.

Error 2: "Microsoft Excel 无法访问文件 xyz.xll" #

This error typically relates to file locks, security blocks, or bitness mismatches:

• Check antivirus quarantine: Windows Defender or third-party antivirus often flags xll files as suspicious after updates. Open your antivirus tool’s quarantine section, restore xyz.xll, and add it to the trusted/exclusion list.
• Kill lingering Excel processes: Updates can leave background Excel processes running that lock the xll file. Open Task Manager → Details, find all Excel.exe entries, end them, then restart Excel and try loading the add-in again.
• Regenerate the xll file: Updates might have corrupted your compiled xll. Clean your project’s bin and obj folders, then rebuild the Excel-DNA project from scratch. If you have a backup, restore the working xll file instead.
• Fix bitness mismatch: If Excel updated from 32-bit to 64-bit (or vice versa), your xll compiled for the wrong architecture will fail to load. Check Excel’s bitness via File → Account → About Excel, then adjust your project’s platform target (x86/x64) in Visual Studio’s project properties and recompile.

Bonus Troubleshooting Tips #

• Right-click your xll file → Properties—if you see an "Unblock" button at the bottom, click it (updates sometimes mark files as untrusted even if they’re local).
• Try launching Excel as an administrator to rule out permission-related access blocks.

内容的提问来源于stack exchange，提问作者Derek Doom