Symptoms of Block and Item Model errors [1.8-11.14.1.1334]

If you haven't already, read this introduction first.

Look in the error console for messages which mention your block or item's name, eg messages like this:
 [Client thread/ERROR] [FML]: Exception loading model yourmodid:block/my_block_model with loader instance, skipping

Did you find any?  If so, hunt through the list of error message below until you find the one which best matches your symptom, then check the list of common mistakes for that error.

Otherwise, unfortunately you have made one of the many possible mistakes which produce no error messages in version 1334.  I can only suggest you look through the list of common mistakes one by one to see if you have made any of them.  Failing that, ask your question at the forum...  and when you've solved it, post me a comment to tell me what the problem was...

Console Error Messages

 [Client thread/ERROR] [FML]: Exception loading model missingtextures:block/mt14_block_model with loader instance, skipping.
com.google.gson.JsonParseException: BlockModel requires either elements or parent, found neither
Parent tag in your block or item model is missing, see MT14, MT15 and MT60 here.

[Client thread/ERROR] [FML]: Exception loading model missingtextures:block/mt15_block_model with loader instance, skipping
com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Unterminated object at line 3 column 6
One of your json files, probably the block or item model, has a syntax error in it, at the given line and column.  This site can help you fix it http://jsonlint.com/.

[10:08:53] [Client thread/WARN]: Unable to load definition missingtextures:mt10_blockname#normal
com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Unterminated object at line 3 column 6
One of your json files, probably the blockstates file, has a syntax error in it, at the given line and column.  This site can help you fix it http://jsonlint.com/.

 [Client thread/ERROR]: Using missing texture, unable to load minecraft:textures/items/mt_item_texture.png
One of your block or item model files has a texture filename or domain which is wrong or in the wrong place.  If the error message contains "minecraft:" then you have probably forgotten to include your modid (MT04, MT63).
For common errors around files see here,
Block texture problems here, MT17, MT18, MT19, MT61, MT62, MT63
Item texture problems here, MT68, MT69, MT70.

[Client thread/ERROR]: Unable to parse metadata from missingtextures:textures/blocks/mt_block_texture_malformed.png
java.lang.RuntimeException: broken aspect ratio and not an animation
Your texture needs to have the same width and height (aspect ratio).

 [Client thread/WARN]: Unable to resolve texture due to upward reference: #all in minecraft:models/block/cube_all
One of your block models, which has cube_all as a parent, didn't define the expected texture #all
see MT13, MT16 here

 [Client thread/ERROR] [FML]: Model definition for location missingtextures:mt61_blockname#normal not found
For blocks:
  a blockstates file problem, see MT02, MT07  here
  or see MT05, MT08 here.
For items:
an item model problem, see MT60, MT61, M62, MT63, MT64, MT65 here

 [Client thread/ERROR] [FML]: Model definition for location missingtextures:mt60_blockname#inventory not found
for blocks a blockstates problem, see MT02  here
for items an itemmodel problem, see MT60, MT64 here