mcrypt win32 install problem ?

Hi, I want to use the mcrypt module and I followed the instructions to install the dll for Win32 users : I copied the libmcrypt.dll file under c:\winnt\system32 I uncommented the "extension=php_mcrypt.dll" in the php.ini I restarted the computer I tried many examples available in the Net. The result is always the same : I can crypt a plain text but I cannot Uncrypt that text. Do you see any potential reason to this? I guess this problem is related to my computer / configuration... current config PHP 4.3.4 Win 2000 PEAR php in fo seems correct about mcrypt