How to fix "Invalid IMEI " after Factory reset? The question is simple "How to fix "Invalid IMEI " after Factory reset?"
After factory reset my phone starts showing "Invalid IMEI" on both SIM slots and I can't call or to being called.

The phone is A738 with Android 2.2.1 and CPU chip is Media Tek MTK6516 416MH

Hope that information is enough.

** UPDATE **

This is the phone
Install the Mobile MTK Engineering Mode app. This will only work on devices with a Mediatek chipset. 


  This Application allow you to run Advanced Setup from Engineering Mode Menu of MTK phones, also called SERVICE MODE  


Other apps which can show the MTK Engineering Mode Menu will probably work too.
If you can't find or don't know your phone's IMEI, then install the Bb IMEI Generator app to generate one for you. If your phone has dual SIM support, you'll need two IMEIs. Note the generated IMEIs by Bb IMEI Generator.
In the Mobile MTK Engineering Mode app go to > MTK Settings > Connectivity > CDS Information > Radio Information > Phone 1.
At the AT+ line:   

  

Enter AT +EGMR=1,7,"ENTER-IMEI-HERE", then tap on 'Send AT Command'. If you have a dual SIM phone, enter AT +EGMR=1,10,"ENTER-IMEI-HERE" then tap on 'Send AT Command' again. Note: The quotes are included. There should be a space after AT.
You should get a notification that the AT Command(s) were successfully sent. Restart your device. You now shouldn't get the 'Invalid IMEI' notification.