Right, firstly, Error::Simple is not a module it is a package that is defined in the file Error.pm. So SomeError.pm should look like

package MyError::SomeError;

use Error;

@ISA = qw/ Error::Simple /;

1;
[download]

Secondly, take a look at your error message - Can't locate MyErrors/SomeError.pm. Note the 's' after 'MyError', which would indicate that the code you're displaying isn't the exact code you're using.

Please see. perlmod and Error before going any further.
HTH

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broquaint