What's wrong with this code?

[Frederic]

Hi,

I can't get the following code to work. It crashes randomly around
[[aDecoder decodeObject] retain];.
I stepped into without success (It never crashes at the same place!).
Sadly, the call stack is (as too often) broken:
(gdb) where
#0  0x8067f83 in objc_msg_lookup ()
#1  0x4057ae14 in __DTOR_END__ ()
#2  0x40539fbf in _OBJC_METH_VAR_TYPE_18 ()
Cannot access memory at address 0x50000.

buggy code:
-initWithCoder:aDecoder
{
        id key = nil;
        id rebuiltProperties = nil;
        NSEnumerator* keyEnumerator = nil;

        self = [super initWithCoder:aDecoder];

        _properties = [[aDecoder decodeObject] retain];
        rebuiltProperties = [NSMutableDictionary
dictionaryWithCapacity:[_properties count]];
        keyEnumerator = [_properties keyEnumerator];
        while ( key = [keyEnumerator nextObject] )
        {
                [rebuiltProperties setObject:[_properties objectForKey:key]
                                        forKey:[NSString keyWithString:key]]; 
/* +keyWithString is
                                                a category that returns a 
NSString which is warranted
                                                to be uniq in the session*/
        }
        [_properties setDictionary:rebuiltProperties];
        return self;
}

The original code, which used to work perfectly was:

-initWithCoder:aDecoder
{
        id key = nil;
        id rebuiltProperties = nil;
        NSEnumerator* keyEnumerator = nil;

        self = [super initWithCoder:aDecoder];

        _properties = [[aDecoder decodeObject] retain];
        return self;
}

Any idea?
Thanks, Frederic