Some flags, for example, the -alpha flag of the polyColorPerVertex command, may return a float array instead of a float. Therefore, if you query the flag argument as follows:
float $a = `polyColorPerVertex -q -a pCube1.vtx[0]`;
You will obtain the following error:
// Error : Cannot convert data of type float[] to float.
The correct way to query this flag is as follows:
float $a[] = `polyColorPerVertex -q -a pCube1.vtx[0]`;