SOME documents saved to Sharepoint won't open via the URL/link

So the background is that we have a document library that files get saved to. When users open the site to access the files, they open up and it is not a problem. However, when the links to these files are emailed out to share with other users, some of the links when clicked cause an error to appear saying: There has been an error while loading form..." The error details say the form template say the user may not have the required permissions to open the file. When I check, the user has the appropriate permissions. Once again, when accessing SharePoint directly, they open up for the very same user without problems. Only the link causes this with SOME files. Has anyone seen this?