The first thing I would suggest is to ensure all remnants of AVG are gone before digging any further.
AVG8 Remover, download tool from here,
http://www.grisoft.com/ww.download-tools there is a 32bit and 64 bit windows version, ensure you use the correct one.
What is your email program ?
Do you have to use SSL (secure encrypted) email ?
It might be better to post the full text of the error.
AVG used to change your email account settings so that it could scan them, I don't know if when you removed it these email account settings were reset to their defaults, I would check your email accounts and ensure the settings are correct.