Poster printing from Solidworks drawing

I produce a solid model of a part in Solidworks (SW) and from this produce a 2D Drawing. I need a full scale print of this and as the part is 1600mm by 200mm I can't print it directly from SW although i can select a custom paper size of the appropriate dimenssions.

I then save it as a .pdf and the file is an exact replication of the drawing.

I then print it as a poster but for some reason extra lines appear on the print which are neither present on the pdf preview or on the originsl drawing.

I have tried it on two computers and two printers with the same result.

One suggestion was to safe it as an image but this was greyed out.

I have done this in the past without this problem but it currently has me beat.