Serialize FileOutPut stream
<p>I have 2 classes: One that simulates a "server" and a second one.
The idea is the server writes a file away with all the required data (usernames, psw, friends, etc...).</p>

<p>Basicly the check login and register user code is all located in the server class and works just fine.</p>

<p>But the problem occurs when i want to pass a List from the other class to the server class.
In the server class this Lists also exists (for initializing (only once singleton)).
This list is used to store all the info.</p>

<p>So the intention is adding the data from other the class to the server class.
(adding in the existing list for example phonenumbers).</p>

<p>But then i get the error while trying to log in: </p>

<pre><code>java.io.InvalidClassException: Implement.Server; 
    local class incompatible: stream classdesc serialVersionUID = ...
</code></pre>

<p>What could be the cause of such a error? Both classes implement Serializable.</p>
