interopability of Public/Private Keys

Question

I am generating public/private keys from Java and want to use them in C#. That for I have read different articles and found, that private keys cannot be exchanged without problem. I have tried two different ways: 1. Export the private key in PKCS#12 format from Java and read it in C# (couldn't export it in that format yet!) 2. Export the needed parameters into an XML file. When I try to use the Java-exported XML file in C#, I get the error that there is invalid data. My questions are now: Is there a better possibility to exchange the key information between different platforms? Is it possible to find out, what 'toXmlString' and 'fromXmlString' in C# are exactly doing? Does anyone have experiences in exporting keys in Java? (I know that Java questions are not supposed to be here but you never know...) Thanks in advance.