Related to : SMS messages just have "null"
Try this,
delete their contact
then
Settings > Applications > Manage Applications > Select the Messaging App
Choose 'Clear Data' and also 'Clear Cache'.
N.B. you will lose all data / txt msg's in your phone
(don't forget to write their number down to save as new afterwards!)
Answer from Blundell on Stack ExchangeHow to unlock iPhone in null without losing data?
If you want to unlock your iPhone in null without losing data, you can refer to the solution introduced in Part 2. Actually, it is a bit possible to fix the iPhone Security Lockout null error without losing data. After unlocking iPhone in null mode, you can restore your data and settings from a backup.
How to enter iPhone passcode in null?
In fact, it is impossible to enter your iPhone passcode in null. When seeing the support.apple.com/iphone/passcode null error, you can try the above solutions to fix the error. Or you can directly using MagFone iPhone Unlocker to remove the screen passcode soon.
How many attempts before seeing iPhone Security Lock null?
Apple allows users to enter the wrong passcode up to 10 times on the iPhone Lock Screen. After making several attempts to unlock your iPhone with the wrong passcode, you will see an iPhone Unavailable message or a Security Lockout screen. However, when more than 10 attempts are made to enter the wrong passcode, your iPhone will be in Security Lockout null.
Related to : SMS messages just have "null"
Try this,
delete their contact
then
Settings > Applications > Manage Applications > Select the Messaging App
Choose 'Clear Data' and also 'Clear Cache'.
N.B. you will lose all data / txt msg's in your phone
(don't forget to write their number down to save as new afterwards!)
You could also check on http://www.google.com/contacts and check if the address book entry for that person is missing some information.