It will be difficult for anyone to help you with this unless they also have a copy of the DLL in question. However, the first thing you should do is add some error checking to your code. You should check that $ApiObject (aweful name!) does actually aquire a value and print out $^E if it fails so that you have a clue as to why.

my $ApiObject = new Win32::API(
    "C:/Documents and Settings/Mdaviesie/Desktop/dver_1.3/fileversion.
+dll", 
    "GetFileVersionTxt", 'PP','I'
) or die "Failed to acquire API: $^E";
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Similarly, assuming that the ->Call(...) is returning, then you should be doing a similar check on the return code.