The original package contains a bug at line 629 where there is the statement
\pgfmathsetmacro{\weightT}{1-\real{\weight}Using once of the different types of umlrelation to link different classes, you get this error
! Undefined control sequence.
\pgfmath@dimen@ ...men@@ #1=0.0pt\relax \pgfmath@The problem with it is the use of \real, which has been moved to other macro in the new viersion of pgfmathparses as reported in this question on TeX-StackExchange