Just to address the concept of
"i would probably put the entire string in a memo field "
Hyperlinks are Memo fields - just with an additional attribute set which causes Access to treat them differently.
Consequently there should be no problem with a long string.
However you say that you "cannot seem to get it to work".
That's less than descriptive of the actual problem.
Is the string correctly assigned, however it fails to launch? If so - saying what?
All important details.
However, looking at your example string, you'll notice it (somewhat unusually for a well named folder structure) contains a octothorpe (#).
These are used as delimiters in hyperlinks between the display text and the URL/UNC actual path. Consequently you're probably just confusing the expression and Access is attempting to launch a file which it thinks is described by the section between the octothorpes.
Consequently (and somewhat ironically) you will be best off implementing the non-hyperlink method as suggested.
(FWIW I personally dislike hyperlinks functionality-wise, though the appearance can be helpfully intuitive for users - that can be achieved by other display means).
Cheers.