New Found Glory Guitarist -- Accused of Online Sex Chatting with Underage Women

New Found Glory guitar player Steve Klein is being accused of video chatting with a minor on an adult website ... but the guitarist says he's totally innocent.

Klein pled not guilty to multiple felony charges back in December ... 2 counts of lewd conduct with a minor under the age of 14, 3 counts of lewd conduct with a minor 14 or 15, 1 count of intent to commit lewd acts with a minor, and 1 count of possession of child pornography -- according to Alternative Press.

Details of the arraignment were just made public ... but on the day it happened, NFG released a shocking statement ousting Steve from the band -- with no explanation about why.

Now, the band says Steve told them about the allegations when they returned home from a tour in Australia ... and they decided to part ways at that point.

Steve's lawyer released a statement saying ALL charges are "derived solely from online consensual video chats" ... he didn't own any child porn ... and Steve believed the girls were older than 18.

The guitar player also says that no one actually knows who the alleged minors are -- including the prosecution, police and defense -- so it's possible they were of age.