chriswyman said

Wont let me add addresses to the address book unless I send them an email. Please can someone help me with this

What are you trying to do in order to add addresses? (You should be able to just right-click on someone's name & address and choose "Add to Address Book" or, from the Address Book window, choose File>>New Address Book Contact.)

What version of Thunderbird are you using?

On what version of which OS are you using it?

Used to work fine, could add them by emailing them or by clicking the star beside their name. Now it wont add, think all up to date it says it is version 45.5.1.

Error comes up when I start it it says

Unable to load address book file abook.mab. It may be read-only or locked by another application. Please try again later

It sounds like your Address Book file may be corrupt.

See:

https://support.mozilla.org/en-US/questions/993178

http://kb.mozillazine.org/Moving_address_books_between_profiles

http://forums.mozillazine.org/viewtopic.php?f=39&t=35466&start=0&st=0&sk=t&sd=a

(I haven't actually had this problem, so I'm not in a good position to guess which of those is most correct, but I think the first is at least most current. Make sure to read all of it before making any changes, and you should probably move or rename abook.mab rather than deleting it.)

Edit: see also, https://bugzilla.mozilla.org/show_bug.cgi?id=495911