I thought the "nexus too small" error would not be shown anymore in A7 - anyways, you are trying to use more memory than currently available for your game. You can increase the amount of memory available (allocate more memory) by increasing the "nexus" parameter which can be found in WED under Map Properties

To use the particles you need to include your particle code in the script file of your level.
Edit: if your particle code is in a C-file (with the .c extension), you can include it using this code:
#include <name_of_the_file.c>
Insert it below the other includes in your level's script file (which is a c-file as well).