That verification is dumb...
... I own Half-Life legally sice a few year.s And i just verified my account this weekend cause maybe someone thought i dont own HL.
SOme people are just to lazy to verify their account
...
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to your problem, you are just missing this sprite. Look for an other sprite trail and copy it and rename it after the missing sprite. I dont know your install steps. so just have to do the Trial and Error method.