Microsoft have released a kb alluding to all the 'showModalDialog' issues customers have been having when using certain Office365 web portal or Outlook Web App and Exchange Admin Center settings when using Google Chrome as their web browser.
The kb is here: http://support.microsoft.com/kb/3001145
The current fix is classed as a workaround, meaning most likely a permanent fix will be put in place at a later date. As this is a deprecated feature it is likely an update to Exchange will fix this issue. We will have to wait and see!
The work around is detailed below:
1. Click Start, type regedit in the Start search box, and then click regedit.exe.
2. Locate and then click the following registry subkey:
3. On the Edit menu, point to New, and then click String Value.
4. Type 1, and then press Enter.
5. Right-click the 1 string value that you created, and then click Modify.
6. In the Value data box, type ShowModalDialog_EffectiveUntil20150430, and then click OK.
If the key is missing entirely under ..\\SOFTWARE\Policies we need to create it.
Seeing as my workstation was missing this I thought I'd take a few screen shots of the process for those small shops that are using Office365 are don't necessarily have any IT experience.
Right click Policies and select New > Key and enter Google
Create sub keys for Chrome and EnableDeprecatedWebPlatformFeatures as shown
Finally enter the key as mentioned.
Oliver Moazzezi - MVP Exchange Server