[Endoperez]

Seems to work for me as well:

#newspell
#name "Summon Hoburgs"
#descr "Cloud of smoke and they appear, masters of surpri-ise..."
#school 0
#researchlevel 0
#path 0 6
#pathlevel 0 1
#effect 1
#nreff 10
#fatiguecost 99
#damage 483
#flightspr -1
#explspr 10143
#range 1
#sound 29
#end

Unfortunately, the cloud of smoke isn't very good. If I change the AoE to 2( or more), every square with Hoburgs in it gets its own cloud, but the number of Hoburgs summons is also doubled (or more).

EDIT: if you change #effect to 10001 and #fatigue to 100, you should get a summoning spell. I did. Works fine.