!heap failed. Invalid type information for ntdll!_HEAP_ENTRY

This could happen if dump was created with 64 bit tools. There is good information on Tess's blog that explains the reason why bitness of the dump matters.

The solution appears to be easy but not obvious.

• I found a wntdll.pdb slightly bigger than mine which contains required symbols and reloaded it with command .reload /f /i ntdll.dll

• and I take the previous build of windbg 6.11.0001.404, in the current one 6.12.0002.633 !heap command still does not work in my case.