unknown decorana error returned (vegan package)

Hi
After trying a simple decorana analysis (from the vegan package) on a simple
data frame which contains no NA's the following error was returned:

tt_decorana(covN)

Error in decorana(covN) : NA/NaN/Inf in foreign function call (arg 1)

Have any vegan users come across this error and know what can be done about it?
Cheers,
J