Previously in July, an error was reported regarding the Document Attachment in which the functionality almost stopped for any user in the system except for the sa user. Any Dynamics GP user is not able to attach and preview attachment.
The error was reported on MSConnect and got enough votes to be solved as soon as possible, and the resolution comes with July Hotfix Round 2, which was released lately in July.
The error was thoroughly illustrated on a previous post Document Attachment Error with GP 2015 R2 - "A Save Operation on table 'coAttachMSTR' has created a duplicate key error"
Build numbers for 2015 are illustrated below:
GP 2015 RTM 14.00.0524
GP 2015 March Hotfix 14.00.0661
GP 2015 R2 14.00.0725
GP 2015 - July Hotfix 14.00.0804
Download Link >> Service Pack, Hotfix, and Compliance update Patch Releases for Microsoft Dynamics GP 2015