Now, upon looking, this seems like a common error, but with no single solution, so here I post my problem and other concerns:

All I get in the output when this breeaks is this: Error parsing XSLT file: \xslt\[COG]Navigation.xslt

How do I get more useful information than that?

All I get when using the umbDebug parameters is this:

Debug from [COG]Navigation

<macro>
  <branchClass>sub</branchClass>
  <maxMenuDepth>1</maxMenuDepth>
  <startingLevel>1</startingLevel>
  <forceHome>1</forceHome>
  <expandChildren>1</expandChildren>
  <selectBranches>1</selectBranches>
  <securityTrimming>0</securityTrimming>
  <recurse>1</recurse>
</macro>

This really isn't that helpful at all, it is just showing me the loaded parameters, I suppose; it would be more useful if I knew the very nature of these 'variables', but alas, I don't (this link seems to target something potentially close to my issue, though: http://our.umbraco.org/forum/developers/xslt/3102-Using-niceurl--Value-was-either-too-large-or-too-small-for-an-Int32-)

How can I A) find out exactly what is wrong here (how t oget an exception/stacktrace)? And B) go about fixing it?

If you want the full XSLT file then I can provide it; it may also be worth noticing that in the link I shared the OP mentions 'NiceURL', the solution is to provide an 'if' condition but it doesn't seem to concern 'NiceURL' at all? Anyway, I tried to apply the fix with little success.