Were you using this handset in Dubai or is this the first time? "Invalid sim" has two main issues, 1. sim lock, 2. sim connector problem.
First, open the battery cover, remove the sim card (if it's inside the battery compartment) and clean the metal contacts of the sim connector using a soft brush or ear bud dipped in alcohol or acetone or spirit. After it's cleaned, let it dry and again reinsert the sim card, install the battery and try again.
If it's been used before, then probably you still have the old sim card, if so install it and try again. If it's ok then borrow a sim card from a friend (for few minutes) or use your old or another available (working) sim card and try again. If both the old sim card and the other (borrowed) sim cards are working without any problem, then there's problem with your vodafone sim card which obstructs it to install on the Handset, perhaps voltage issue, in that case, you better get another replacement from Vodafone.
Or if the old one which you were using works, then your phone is sim locked, try to reset it using the default code 1122 or 3344 or 1234 or 5678 (should be on the manual) [click here for more info about china mobile codes]
. To do this, go to settings, select "Restore" and enter the code, proceed forward giving positive inputs "yes" or "Ok".
After it's restarted, try again with all the sim cards.
If all the sim cards show the same error, then the handset might needs to be repaired or need to be replaced.
If you need further help, let me know.
Thanks for using FixYa.