Is there a list of Excel VBA syntax differences in Compatibility mode?

We have an old .xls file with macros that I was asked to convert to .xlsm (company policy blocking .xls files). The problem is that after the conversion, some of the VBA macros no longer work. My guess is that this is due to the change from Compatibility mode in the original file.

Here is an example that used to work and now does not - the syntax is actually wrong according to the current documentation, but it used to work and now does not .. and I did not expect syntax changes when changing a file extension...

With Sheets(StartArk)
    .Rows("A9:IV10000").Clear
    .Columns("A:IV").ColumnWidth = 8.43

I have two questions:

• Is there a list of syntax changes between the two VBA versions?
• Is there a way to have an .xlsm using the old syntax?