open Step7 v5.3 project in v5.1

Hello guys, we've got a plc program that is made in STEP 7 v5.3, however on our PG is installed STEP7 v5.1+SP2. Now, when we try to open it, we cant reached to hw configuration, symbol table and blocks. Is there any way from STEP7 v5.3 to save project as STEP7 v5.1. Guy wo has written these programs have Step 7 v5.3, but don't know how to save it so it could be opened in Step7 v5.1 + sp2.

Thanks for help

I was in a similar situation last year.
You can view and change the code, you cannot and should not try to change the hardware.
I don't think you can backwardly save. Also, some of the hardware that is used may not be compatible with S7 5.1.

solved!

Yes, hardware was the reason, it seems that V5.1 doesn't have types of CPU in library which is used in V5.3 project. I found somewhere that SP4 will solve the problem although I'm not sure if new authorisation is needed.
Regards, Pandiani