My question is this: can I easily find where the problems are? I have over 30 mods and I don't know what exactly I'm looking for...
One way to find out what plugin references these problematic things is to use some search application like http://www.inforapid.de/html/searchreplace.htm, which can be used, for example, to search for the string "SC_Gnisis_guard1" in your "Data Files" directory.
"cruel_spark_ma_en" is probably from the official Bethesda plugin "Area Effect Arrows".
"SC_Gnisis_guard1" is probably from LCV (Living Cities of Vvardenfell).
Then you should probably double check that these have been installed correctly and that they aren't conflicting with other plugins.