Please make sure that Dimensions was installed under the Domain Admin account that the user in question has sufficient read/write permissions to the Dimensions folders.
If this has been checked and the message is still presenting itself, try the following:
Select to Add New Printer.
Select Local Printer, making sure Auto detect deselected is un-ticked.
On Prompting for Port select the Access PDF Port.
Select save to disk, and browse to the Dimensions 2.5xxx software directory.
Double click on Amyuni.inf file.
Finally, Name the Printer as Access UK Ltd.PDF Printer.