If you get this error trying to set and hit a breakpoint, there are a couple of things to look for to resolve it. Typically what this error means is that the compiler cannot find debug information for the file you are trying to set a breakpoint in.

The first thing to check is that you have compiled the assembly in debug mode.

If you build the assembly in Release mode it will not generate the necessary debug information. Also be aware that there are two modes the compiler can use to generate the necessary program database (pdb) file for debugging, but only one of them actually enables incremental linking of the debug info.

/debug:full or /debug:pdbonly. Building with /debug:full generates debuggable code. Building with /debug:pdbonly generates PDBs but does not generate the DebuggableAttribute that tells the JIT compiler that debug information is available.

Depending on how you are building your solution you either need to look at the msbuild file or if you are building from within Visual Studio you can right click the project file and select properties. Then select the Build tab, and then the Advanced button. You will get the following dialog (VS2008, 2005 may look slightly different.)

Notice under Output the line for Debug Info, make sure this is set to full. The other values available are none, and pdb-only. Neither of the latter two values will result in debuggable code.

The next most common cause is that the [assemblyname].pdb file is not being copied or updated correctly to the bin folder of the startup project in a multi project solution.

You can manually copy the assembly file and the pdb file from the bin folder of the assembly you want to debug into the bin folder of the startup or calling project. Or into the web application bin folder if you are calling the assembly from a web application.

Thanks to Adam McKee of Ironworks who recently reminded me of the fix for this problem. I have put the information here to hopefully help the next person.

Cheers,

Robert Porter