Just for further info.
User A can have an issue dragging an email or file into CRM but user B can attach that file or email!? 
However, as time progresses the volume of attachments that generate the error increases and the users who get the error also increases to the point where a server reboot must be performed.

Have you ever found out why this happened? Or a solution to it other than a server reboot?

I am having the same problem but a reboot didn't help it. 

This is the only reference to this particular problem that I have been able to find.

Just found this issue this week in a customer.

In this case the cause was the CRM server run out of space in HDD, due to the big logs generated by CRM itself.  So, the solution is easy.

I guess this is not your case.

Anyway, I will ask Sage CRM about give us the possibility to disable some of the logs that currently cannot be disabled.

Otherwise, CRM logs need to be reviewed periodically and manually remove it.

I've found 4 possible reasons:

• The attachment size exceeds the limit set in the 'File Size Limitation' in the Documents & Reports Configuration
• The attachment name has an 'unsupported character' in it. I've had issues with % and $.
• The actual attachment is not deemed as a valid file. This has been where a PDF has been created using an unsupported application and the header details are not as expected.
• The final one, which should be resolved with a reboot, is that apparently Apache Tomcat has a memory leak and once it hits the limit it causes the 200 error. You'll start seeing this initially on large attachments, so a user may fail when attaching a 10Mb file but it works fine on a 3Mb file!! This will then start to affect all files, so when only 1 user initially reports the issue and others work OK, it spreads..
  
  

Hope this help.

Roger

And as 'Tinojovani' has already posted, disk space 

Thank you all for your feedback, it was helpful.  It seems we had two problems going on 1) The memory leak which causes the problem in the first place, and 2) The account I was using to reboot the server was missing some permissions.  It could start Sage, but very soon services would crash again making it look like the reboot wasn't working. When we tried it with a different account, the reboot fixed it.