Cannot generate Doxygen diagram - c++

Question

I am trying to draw an interaction diagram with Doxygen, using the external Mscgen utility.
This is the source file:
/// test.h
/** Interaction diagram.
* Test.
* \msc "Test interaction diagram"
* A,B,C;
* B->C;
* A<-B;
* \endmsc
*/
class A {};
class B {};
class C {};
I installed the mscgen.exe executable, and I set its path in the environment variable.
When running Doxygen, from its log this is all I get in relation to interaction diagrams: "Searching for msc files...".
The final Doxygen output contains a place holder for a missing interaction diagram, and the "Test interaction diagram" label.
I must be missing something in the Doxyfile file. How can I make Doxygen call the mscgen.exe executable?
Looking at the PNG files generated, the one Doxygen is looking for is missing, so I suppose mscgen.exe has not run at all.
This is the Doxygen generated HTML code block:
<div align="center">
<img src="../../msc_inline_mscgraph_1.png" alt="msc_inline_mscgraph_1" border="0" usemap="#msc_inline_mscgraph_1.map">
<map name="msc_inline_mscgraph_1.map" id="msc_inline_mscgraph_1.map"></map>
<div class="caption">
Test interaction diagram</div>
</div>

Answer 1

Try removing the caption. I have the same problem on Windows. I do not have other platforms handy to compare results and see if it is a Windows-only problem. When I do:
#msc "hello, world"
a, b;
a => b;
#endmsc
The figure does not generate. If I remove the caption, like this:
#msc
a, b;
a => b;
#endmsc
The figure generates, but there is no caption. When the caption is present, I see the error:
error: failed to open map file path-on-my-local-computer-redacted/docs/html/inline_mscgraph_2.msc.map for inclusion in the docs!
The interesting part is that the file is not generated when there is no caption either -- the difference is that Doxygen does not seem to care that the map file does not exist. I do not seen an obvious option that controls map file generation.
Sorry, for just a partial answer several months after the original question. I got here Google searching for an answer the same question and hope this will at least let others get sequence charts without captions.

Answer 2

I had the exact same problem and found that a syntax error in the msc-part was the reason. Once I got it error-free, it all build well.
It take me a while to identify the problem. A search took me to a guy's thread "Problem with msc graph" who had the same problem and the solution:
[...]
If there is a syntax error in an msc tag then At the end of the
generation run I get the following error message:
error: failed to open map file [...]