Dumb question, but have you tried PrecacheModel() instead of PrecacheDecal()? AFAIK, it used to be how I always pre-cached texture files. Also, make sure you include .vmt in the call to PrecacheModel()
eg:
GOOD
Code:
g_iSprite = PrecacheModel("materials/test.vmt", true);
BAD
Code:
g_iSprite = PrecacheModel("materials/test", true);
If that doesn't work, maybe try this?
Code:
g_iSprite = PrecacheDecal("materials/test.vmt", true);
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