IncompatibleClassChangeError, occurs with several mods.

[PeterGrace]

See below example of stack trace. Is this a problem with the other mods or is there a base problem in Register? I am running the latest Register.jar out of the dist/ folder, and running craftbukkit 1321.

md5sum:
7058e31c3a7b082a77d03c9f07c76d32 Register.jar

17:32:10 [SEVERE] Exception in thread "Thread-536"
17:32:10 [SEVERE] java.lang.IncompatibleClassChangeError: Expected static method com.nijikokun.register.payment.Methods.getMethod()Lcom/nijikokun/register/payment/Method;
17:32:10 [SEVERE] at com.tarpix.MCStatsPlus.model.PlayerStatistics.getCurrency(PlayerStatistics.java:186)
17:32:10 [SEVERE] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
17:32:10 [SEVERE] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
17:32:10 [SEVERE] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
17:32:10 [SEVERE] at java.lang.reflect.Method.invoke(Method.java:601)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.reflect.Accessor$GetterSetterReflection.get(Accessor.java:339)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.reflect.Accessor.getUnadapted(Accessor.java:132)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.reflect.TransducedAccessor$CompositeTransducedAccessorImpl.hasValue(TransducedAccessor.java:236)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.property.SingleElementLeafProperty.serializeBody(SingleElementLeafProperty.java:90)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:341)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsSoleContent(XMLSerializer.java:582)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:323)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:483)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:308)
17:32:10 [SEVERE] at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:236)
17:32:10 [SEVERE] at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:95)
17:32:10 [SEVERE] at com.tarpix.MCStatsPlus.reporting.StatsSerializer.statsAsXml(StatsSerializer.java:100)
17:32:10 [SEVERE] at com.tarpix.MCStatsPlus.model.StatsModel.saveUserFiles(StatsModel.java:169)
17:32:10 [SEVERE] at com.tarpix.MCStatsPlus.model.StatsModel$1.run(StatsModel.java:129)
17:32:10 [SEVERE] at org.bukkit.craftbukkit.scheduler.CraftWorker.run(CraftWorker.java:34)
17:32:10 [SEVERE] at java.lang.Thread.run(Thread.java:722)

[PeterGrace]

Oh, forgot to mention that this is in java 1.7.

[Acrobot]

That means that one of your plugins uses different version of Register (the older one).
McStats uses right Register version, however some of your other plugins uses the older.