I could not find anything like tr557. Do you mean BC557?

If you are using a PNP transistor, you are doing a very basic mistake. For a PNP transistor,

1) VB < VE-0.7 to trun on.
2) VB > VE-0.7 to trun off.

When you use 12V relay, condition 1) above is always fulfilled no matter your micro emits a logic '0' or '1'.

When you use a 5V relay, your micro can satisfiy both the above condition.

Solution:

1) Use a NPN transistor.
2) If you must use a PNP to control the realy, you can use a NPN to drive your main PNP tansistor. You can see a similar circuit here.

http://www.8052.com/forum/read.phtml?id=84161