We are using CRM 2013 SP1. I have been noticing this behavior in the last 2 months while using both IE and Chrome.
At times when I try to reply to an email - even before I start typing my reply - if I try to save the email just with the content I get to see the following box

As you can imagine - there is no error log. At times (not always) I get the following error message that gets compiled to be send to Microsoft.
CrmScriptErrorReport>
<ReportVersion>1.0</ReportVersion>
<ScriptErrorDetails>
<Message>Unable to get property 'nextSibling' of undefined or null reference</Message>
<Line>7</Line>
<URL>/_common/global.ashx?ver=1112044343</URL>
<PageURL>/main.aspx?etc=4202&extraqs=%3fetc%3d4202%26id%3d%257bEB3A2861-CC7D-E711-9F14-0050568B3005%257d&pagemode=iframe&pagetype=entityrecord</PageURL>
<Function>anonymousr:Unabletogetproperty'nextSibling'ofundefinedornullreference</Function>
<CallStack>
<Function>anonymousr:Unabletogetproperty'nextSibling'ofundefinedornullreference</Function>
</CallStack>
</ScriptErrorDetails>
<ClientInformation>
<BrowserUserAgent>Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.3; WOW64; Trident/7.0; .NET4.0E; .NET4.0C; .NET CLR 3.5.30729; .NET CLR 2.0.50727; .NET CLR 3.0.30729; InfoPath.3)</BrowserUserAgent>
<BrowserLanguage>en-US</BrowserLanguage>
<SystemLanguage>en-CA</SystemLanguage>
<UserLanguage>en-CA</UserLanguage>
<ScreenResolution>1920x1080</ScreenResolution>
<ClientName>Web</ClientName>
<ClientTime>2017-08-10T09:16:22</ClientTime>
</ClientInformation>
<ServerInformation>
<OrgLanguage>1033</OrgLanguage>
<OrgCulture>1033</OrgCulture>
<UserLanguage>1033</UserLanguage>
<UserCulture>1033</UserCulture>
<OrgID>{B13FC7A6-21DE-E411-8022-0050568B3005}</OrgID>
<UserID>{297FE288-D7C1-E411-8E18-0050568B3005}</UserID>
<CRMVersion>6.1.0.581</CRMVersion>
</ServerInformation>
</CrmScriptErrorReport>
Has anyone faced this issue ?
Hasibur Rahman