"mscorlib.pdb not loaded" yet the mscorlib.dll is NOT missing

I am running my application in VS2012 and I am getting a runtime error;

When I look in the "Original Location" I see mscorlib.dll, but not mscorlib.pdb.

Why is this happening and how do I fix it?

Goto Tools, Options, Debugging, General, Enable Just My Code

This will prevent the debugger from trying to launch on a Internal .NET Framework Assembly.

Goto Tools, Options, Debugging, Symbols and set a cache location. Then hit load in the above and it will fetch the necesary symbols for you and store them in the cache location you provide.

Microsoft's compiler tools create symbols in separate files with a .pdb extension (program database). This allows them to create detached symbols for release binaries. With a symbol server, your IDE can fetch the symbol file matching the specific version of the DLL during debugging. You can configure this system for your own product binaries as well which can be very useful for post-mortem debugging any crashes on end-user machines.

See Microsoft's documentation for more details about using their public symbols.

I had this issue when I was using a static variable, whose value is assigned off a static method.

So, whenever I ran the application, this line of code threw exception. If you place a debug point on this (like I did), you will notice the exception being thrown.

The best Solution to solve this error is:

1: Open App.config file.

2: Paste this useLegacyV2RuntimeActivationPolicy="true" code in the startup tag.

3: Save it.

Now the error would disappear. Moreover see Image. I have done this for you.

This happened to me for a different reason: I had referenced an old version of NLog (2.0) and needed to reference version 4.0, instead.

In a VB console app, in my case it was none of the above.

Just doing a string calculation in the Dim declarations before my subs.

The offending code:

Dim FylPrefix$ = Fyl.Substring(0, Fyl.LastIndexOf("."))

Moving this calculation into the sub it was needed in fixed it! GERONIMO!!

In my case the exception began to appear after I changed the "Assembly name" in the "Application" tab of the properties window. If that's the case with you try reverting to the original name and see if the exception disappears. Perhaps the reason for this was that the new name did not match the AssemblyTitle in AssemblyInfo.cs.

This can happen when you initialize a variable in your class declarations and that initialization throws an exception:

class Program
{
    static OracleConnection ora = getOracleConnection(); 
    
}
static void main(string[] args) 
{
    ora.Open();
}
static OracleConnection getOracleConnection()
{
   OracleConnection orax = new OracleConnection(description=(host=myHost)
    (port=1521)(protocol=tcp))(connect_data=(sid=mySid)));user id=user;password=pw;
}

If an exception is thrown by getOracleConnection() you can get this error. Move your assignment (but not necessarily your declaration) inside of main (where it belongs anyway), and you will get the actual exception that is causing the error instead of the mscorlib error.

if you have this type of project runtime error in visualstudio Answer:Cntr+Alt+E open Exception window Uncheck All chechboxes Must and shoud its working written by B sriram Mca Giet College rajahmundry, east godavary ,2014 batch