The Dell downloads show an Intel Serial I/O driver. Its not clear if this is the hardware device for the RS232C I/O or not, but if it is its a later driver than the default Windows driver. The 2006 date on the Microsoft driver is a generic date, there are several devices that have similar old dates. e.g. the Microsoft Firewire driver that I use on my recording studio system also has a 2006 date but its the "latest" driver.
By the way, the "Workstation" section of the forum is for Precision hardware support.
Dell forum member since 2002
Dell Inspiron 15 - 5577 Laptop
Home Built Desktop PC with ASUS ROG Z170, i7 6700K CPU
Windows 10 64 bit Pro and Windows 10 Insider Program Beta Versions. SSD drives. Cakewalk by BandLab and Studio One 4.1 Recordng Studio Software.
Dell S2719dgf Monitor
Member of Nashville based R.O.P.E.
Try enabling hardware flow-control.
Check protocol settings match on both ends.
Use high-quality cables.