You can find the following entry in the ULS-Log:
Solutions2Share.Solutions.CollaborationManager.EventReceivers.WorkspaceListEventReceiver.ItemAdding: Item does not exist. It may have been deleted by another user. ExceptionType: 'ArgumentException' ExceptionMessage: 'Item does not exist. It may have been deleted by another user.' StackTrace: '
at Microsoft.SharePoint.SPList.GetItemById(String strId, Int32 id, String strRootFolder, Boolean cacheRowsetAndId, String strViewFields, Boolean bDatesInUtc, Boolean bExpandQuery)
at Solutions2Share.Solutions.CollaborationManager.Services.Functions.GetTemplateByWorkspaceField(TemplateLookup templateField, SPSite site, Boolean sync)
at Solutions2Share.Solutions.CollaborationManager.EventReceivers.WorkspaceListEventReceiver.ItemAdding(SPItemEventProperties properties)' Source: 'Microsoft.SharePoint' TargetSite: 'Microsoft.SharePoint.SPListItem GetItemById(System.String, Int32, System.String, Boolean, System.String, Boolean, Boolean)'
Please navigate to the Template Library and add the Users / Group to the library permissions with Read Permission Level