[Exim] Exim goes crazy

Hi there,

Without any reason our exim installation starts to give the following
error message:
"D=system_aliases defer (-18): failed to open /et#/aliases for linear
search: No such file or directory"

Although exim seems to work fine for several weeks, it once in a while
turns wild and gets /et#/aliases instead of the default /etc/aliases

Any idea on where this problem might be generated?

Armin