First off, thats tropic vendetta. Second, it's a missing particle since this map is really old and outdated
I've renamed your thread because it isn't emp_isle, it's a custom map named emp_tropicvendetta_rc4. After a quick check on my own client it looks like the server hasn't forced a download of the map's particle manifest file - particles\particles_emp_tropicvendetta_rc4.txt is missing.
It looks like it's actually a problem with the particle itself, both the NF and BE explosion particles, as it shows up in the particle preview. I have no idea what could be going wrong here but maybe someone with particle understanding could adjust it and a new .pcf could be distributed?
The particle is for an older engine version, its supposed to be a massive explosion someone made from an old hl2 grenade explosion particle variant that was never used. iirc
lol... never saw that... - but my instalation of empires is from long long ago (backup) - so maybe i have that particle/definition file thats missing?