Much more information is needed. Are you using Thunderbird or another e-mail program? Are you trying to write an email from the email program or trying to do it clicking on a link in a web page in your browser?

 What "flavor" of Linux and what desktop do you use (Suse, Ubuntu, Mint system, etc., Gnome or KDE desktops)? Are the web browser and email program set as the default programs or their type? There are many Linux email clients. No two are identical. 

 Step by step, what steps are you doing to try to write or forward an email?

I use yahoo for email & ubuntu. Forward-- I open an email, click on forward arrow. Compose window comes up & says loading original email. Then says Yahoo! Mail found the original email, but encountered problems displaying it. Please try again later. Email--- Click on compose, same thing, everything is frozen. TO: BC: BCC: takes no email addresses, body of email will not take typing.

I can't duplicate your problem, but I use OpenSuSE Linux.

I only found a couple of suggestions that someone with a similar problem posted. One stated that if he changed from rich text to plain text, it solved his problem. I'll add an image of the setting from the Yahoo web page.

The other stated that cleaning all cookies, temp files, and history fixed her Yahoo Mail. For that, go to "Edit>preferences" and choose the "Security tab. There is an option for clearing all history and cookies.

Other than that, I found where a lady had the same problem and complained to Yahoo. She got a response and Yahoo claimed that they had fixed her account.

Wish I could have been more help.

Solved the problem. It was the program Ghostery. Thank u for all your help.