Failed to read the value of field ... using reflection

Hello,

we got following exception.

Can you explain me, what is the reason of this exception?

Caused by: com.objectdb.o.UserException: Failed to read the value of field field com.btc.ep.expression.formula.bl.dmos.Valuation.variableSettings using reflection
    at com.objectdb.o.MSG.a(MSG.java:77)
    at com.objectdb.o.UMR.s(UMR.java:938)
    at com.objectdb.o.UMR.YU(UMR.java:613)
    at com.objectdb.o.UML.YU(UML.java:551)
    at com.objectdb.o.MMM.H(MMM.java:1191)
    at com.objectdb.o.UTY.K(UTY.java:1505)
    at com.objectdb.o.UTY.L(UTY.java:1432)
    at com.objectdb.o.ENH.d(ENH.java:104)
    at com.objectdb.o.LDR.d(LDR.java:832)
    at com.objectdb.o.LDR.ZU(LDR.java:1067)
    at com.objectdb.o.RTT.r(RTT.java:270)
    at com.objectdb.o.RTT.q(RTT.java:251)
    at com.objectdb.o.RST.p(RST.java:183)
    at com.objectdb.o.RTT.g(RTT.java:136)
    at com.objectdb.o.RST.g(RST.java:26)
    at com.objectdb.o.TSK.b(TSK.java:146)
    at com.objectdb.o.TSK.c(TSK.java:96)
    at com.objectdb.o.TSM.a(TSM.java:88)
    at com.objectdb.o.MST.aw(MST.java:637)
    at com.objectdb.o.MST.ZL(MST.java:575)
    at com.objectdb.o.WRA.ZL(WRA.java:281)
    at com.objectdb.o.LDR.u(LDR.java:585)
    at com.objectdb.o.LDR.Zp(LDR.java:475)
    at com.objectdb.o.OBC.Zp(OBC.java:1122)
    at com.objectdb.o.RSL.b(RSL.java:323)
    at com.objectdb.o.RSL.get(RSL.java:171)
    ... 57 more
Caused by: java.lang.IllegalArgumentException: Can not set [Lcom.btc.ep.expression.formula.bl.dmos.VariableSetting; field com.btc.ep.expression.formula.bl.dmos.Valuation.variableSettings to [Ljava.lang.Object;
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
    at sun.reflect.UnsafeObjectFieldAccessorImpl.set(UnsafeObjectFieldAccessorImpl.java:81)
    at java.lang.reflect.Field.set(Field.java:764)
    at com.objectdb.o.UMR$b.D(UMR.java:1084)
    at com.objectdb.o.UMR$a.x(UMR.java:1019)
    at com.objectdb.o.UMR.YU(UMR.java:607)
    ... 80 more

It may indicate partial enhancement.

As you use enhanced classes, make sure that all persistable classes are enhanced as well as other classes that access directly persistent fields of persistable classes.