问题的原因可能是您在解决方案中混合添加了对DLL文件和项目的引用。

如果你有项目A、B和C:

A引用B和C作为解决方案中的项目。 B引用C作为DLL文件(引用文件)

您可以单独构建每个项目，但无法重新构建以以下内容结尾的解决方案:找不到元数据文件“C.dll”。

在解决方案中将引用从文件更改为项目会有所帮助。

In my case it happened to me when I was referencing NuGet packages locally and moved their directory to somewhere else, I changed the path inside NuGet.Config but unfortunately I discovered that I should change the .csproject files manually to update the reference path, but the error message CS0006 was way far from describing this problem. Generally it also happens when there is a reference to DLL that couldn't be found, to be able to identify issue search your references in the project with the problem you will find some references with warning icon associated with them, try fixing those and it should work as expected.

好吧，我的答案不只是所有解决方案的总结，但它提供了更多。

节(1):

一般解决方案:

我有四个这样的错误(“元数据文件找不到”)，还有一个错误是“源文件无法打开(“未指定的错误”)”。

我试图摆脱'元数据文件找不到'错误。为此，我阅读了许多文章，博客等，发现这些解决方案可能是有效的(总结在这里):

Restart Visual Studio and try building again. Go to 'Solution Explorer'. Right click on Solution. Go to Properties. Go to 'Configuration Manager'. Check if the checkboxes under 'Build' are checked or not. If any or all of them are unchecked, then check them and try building again. If the above solution(s) do not work, then follow sequence mentioned in step 2 above, and even if all the checkboxes are checked, uncheck them, check again and try to build again. Build Order and Project Dependencies: Go to 'Solution Explorer'. Right click on Solution. Go to 'Project Dependencies...'. You will see two tabs: 'Dependencies' and 'Build Order'. This build order is the one in which solution builds. Check the project dependencies and the build order to verify if some project (say 'project1') which is dependent on other (say 'project2') is trying to build before that one (project2). This might be the cause for the error. Check the path of the missing .dll: Check the path of the missing .dll. If the path contains space or any other invalid path character, remove it and try building again. If this is the cause, then adjust the build order.

节(2):

我的具体情况是:

我尝试了上面所有的步骤，并重新启动了几次Visual Studio。但是，这并没有帮助我。

所以，我决定摆脱我遇到的其他错误('源文件无法打开('未指明的错误')')。

我看到一篇博客文章:TFS错误-源文件无法打开(“未指明的错误”)

我尝试了那篇博客文章中提到的步骤，我摆脱了“源文件无法打开(“未指明的错误”)”的错误，令人惊讶的是，我摆脱了其他错误(“元数据文件无法找到”)。

节(3):

这个故事的寓意:

尝试上文第(1)节中提到的所有解决方案(以及任何其他解决方案)来消除错误。如果没有解决问题，按照上面第(2)节中提到的博客，从.csproj文件中删除源代码控制和文件系统中不再存在的所有源文件的条目。

我看到这个错误是因为我在我的代码中有以下一行(看起来我仍然在SQL模式下思考):

if(myVar is null)
    DoSomething();

Visual studio(2017)在设计或编译时没有报告错误，但项目不会构建，并给出了“missing .dll”错误。将错误的行改为:

if(myVar == null)

问题解决了。

几年后再回到这个问题，这个问题很可能与Windows的最大路径限制有关:

命名文件，路径和命名空间，最大路径长度限制

检查主项目的.csproj文件。如果您在解决方案中删除项目或更改引用，Visual Studio不会清除这些问题。

我在.csproj文件中引用了三次旧项目，编译器向这些已删除的项目显示了此错误。