chains with he4

[Andrea Maselli]

Hi,
i've a problem trying to use cosmomc for estimate helium abundance with mock data. I modified source code to add a new parameter (he4) and i run a single chain with a prior on he4 but after a few hundred of points chain stops with the following message

updating proposal density
Proposal matrix has negative or zero eigenvalues

can anyone help me

thanks a lot,
Andrea