The player can read measures of different length, but the chords within the measure need to be properly spaced to indicate what beat they occur on.
Currently, supported note length values for chords are whole notes, half notes, quarter notes and (in 3/4 time signatures) dotted quarter notes.
If an error message appears about chord spacings when you play your own charts, this means that the player is not able to calculate the length of chord relative to the other chords in the same measure. It is important to position the chords spatially so they clearly indicate their length.
An example of unclear chord length.
While this will play successfully.
If you leave the first beat or beats of a measure empty they will simply be ignored. For example, if you want the the first two beats of a measure to continue playing the chord from the previous measure, add slashes to those two beats.
This will play correctly:

while this:

will sound like:
Note: Blank measures are ignored completely, this includes empty space (no bar lines) anywhere in a system, for example, the empty space before a 2nd time measure where it starts mid-system to line up vertically with the 1st time bar. This means you’ll have to add the % (repeat bar) sign if you want the chord from the previous bar to repeat.
Note on Error Messages
After pressing the Play button, the audio begins to construct before it starts playing. If there are problems with your chart, error messages tell you what is wrong and the bar number of the error. It counts from the first bar and keeps on counting up through any repeated sections.
For example, if a song has a repeated A section of 8 bars, then a B section of 8 bars and an error is found in bar 18, this is the 2nd bar of section B
(A8 + A8 = 16 + B2 = Bar 18)