I am trying to fit my data, attached,  with the following model

CutOff <- 0

fit.full <- lme(fixed= zGrade ~ Rep + ISE +Yfrm7A +Ufrm7A +Female +White
+HSGPA +MATH +AP_TOTAL +Years +Course +
                 Course*Rep + Course*ISE +Course*Yfrm7A+Course*Ufrm7A
+Course*Female +Course*White +Course*HSGPA +Course*MATH +Course*AP_TOTA
L+Course*Years,
                random= ~1|SID,
                data = Master.complete[Master.complete$GRADE >= CutOff,])
 I get the following error
Error in MEEM(object, conLin, control$niterEM) :
  Singularity in backsolve at level 0, block 1


when I take out
+Course*Yfrm7A+Course*Ufrm7A
and just use
fit.full <- lme(fixed= zGrade ~ Rep + ISE +Yfrm7A +Ufrm7A +Female +White
+HSGPA +MATH +AP_TOTAL +Years +Course +
                 Course*Rep + Course*ISE
+Course*Female+Course*White+Course*HSGPA+Course*MATH+Course*AP_TOTAL+Course*Years,
                random= ~1|SID,
                data = Master.complete[Master.complete$GRADE >= CutOff,])
  I don't get an error

I think this is because when Course == P7A  Yfrm7A==Ufrm7A==0.  I am not
sure how to work around this.  any suggestions would be welcome.

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