CFA in R: The variance-covariance matrix of the estimated parameters (vcov) does not appear to be positive definite. What is the problem?

Question

I am trying to calculate a CFA for the Theory of Planned Behaviour (TPB). I have split the 4 factors (Attitude, SubNorm, PBC, Intention) into inverted and non-inverted items. Enclosed is the measurement model.

N = 75. The items were rated on a scale of 1-7.

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However, after I run the second part (categorical part), I receive a warning message that says:

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Do any of you know the problem and what can be done?