Got it. The crash indeed happens in Serum.
However what is more important is that you appear to be using a very old OpenMPT version (1.23, more than five years old). Unfortunately we cannot give support or provide bugfixes for anything but the latest versions of OpenMPT. Many things in OpenMPT have been improved since version 1.23, so it is quite likely that if there was some incompatibility between Serum and OpenMPT, it has already been fixed in the meantime.
On a side note, OpenMPT 1.29 will be released soon, and it will provide a much more stable plugin bridge than before, which should make it more feasible to isolate all VST plugins so that they cannot crash the main OpenMPT process anymore.