dlmread is able to read that format without a problem. Checking, matlab2021a is able to load('dynam') as well. I don't see any particular reason load shouldn't be able to read it, so it may be worth a bug report.
correction, it appears dlmread ignores the D. e.g., the last line in the file is:
12.00000 .511026D-02 .334856D-02 .101089D-03
read in by matlab as:
12.000000000000000 0.005110260000000 0.003348560000000 0.000101089000000
but dlmread as:
1.200000000000000e+01 5.110260000000000e-01 3.348560000000000e-01 1.010890000000000e-01
so, this does seem to be a compatibility bug.