[R] SEM error

[Kes]

Dear All,
I am new for R and SEM. I try to fit the model with Y (ordinal outcome), X
(4 categorical data), M1-M3 (continuous), and 2 covariates (Age&sex) as a
diagram. 
library(polycor)
model.ly <-specify.model()
1: x -> m1, gam11, NA
2: x -> m2, gam12, NA 
3: x -> m3, gam13, NA 
4: age -> m1, gam14, NA 
5: age -> m2, gam15, NA 
6: age -> m3, gam16, NA 
7: sex -> m1, gam17, NA 
8: sex -> m2, gam18, NA 
9: sex -> m3, gam19, NA 
10: x -> y, gam20, NA 
11: m1 -> y, gam21, NA 
12: m2 -> y, gam22, NA 
13: m3 -> y, gam23, NA 
14: age -> y, gam24, NA 
15: sex -> y, gam25, NA,
16: m1 <->m1, psi11, NA
17: m2 <-> m2, psi12, NA
18: m3 <-> m3, psi13, NA
19: m1 <-> m2, psi21, NA
20: m1 <->m3, psi22, NA
21: m2 <-> m3, psi23, NA
22: Y <-> Y, psi24, NA, 

hcor <-function(ly) hetcor(ly, std.err=FALSE)$correlations
R.ly <-hcor(ly)
sem.ly <- sem(model.ly, R.ly, N=174)

Error in sem.default(ram=ram, S=S, N=N,…………………………)
The model has negative degree of freedom = -12

First, I do not know what the mistake is. Second, is this correctly modeling
my diagram?  Any suggestions would be appreciated. 

Thank you,
Kesinee 
http://r.789695.n4.nabble.com/file/n3340497/path.gif.png 

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