Disputed Usages - Urgent! Please help!

Can someone please help pointing out the 'disputed usages' in the following sentences:
1) He was out at a meeting and couldn't be contacted all day.

2) His second plan is not as imaginative as his first but it is more credible.

Thanks,
Eva

[Casiopea]

Coordinating conjunction; e.g., and, but join two independent clauses.

1a) He was out at a meeting and he couldn't be contacted all day.

If the clauses share the same subject, the subject of the second clause is often omitted for the sake of efficiency - it's redundant:

1b) He was out at a meeting and couldn't be contacted all day.

If the clauses are connected in thought (e.g., hold a cause & effect relationship), adding a comma isolates the 2nd clause from its context. The second clause reads like an after-thought here:

1c) He was out at a meeting, and (he) couldn't be contacted all day.

[evaho88]

Thanks very much Casipoea. So do you mean both sentences have the same problem with comma? And should be rewritten as:

1) He was out at a meeting, and couldn't be contacted all day.

2) His second plan is not as imaginative as his first, but it is more credible.

I once thought #2 had the problem of 'Pronoun whose antecedent is a possessive', my thought is:
In this sentence, ‘his first’ lacks any clear antecedent – it certainly cannot refer back to ‘his second plan’, thus the sentence must be ungrammatical, or at least meaningless, unless a previous sentence provides an antecedent, for example, ‘The Professional Business Plan in 2006’, is a clear antecedent.

Would you like to comment on this. Thanks

[Casiopea]

Firstly, there isn't an antecedent problem. Second, given the semantic relationship between the two clauses in 1) and 2) respectively, I would suggest that you not use a comma:

1) He was out at a meeting and couldn't be contacted all day.

2) His second plan is not as imaginative as his first but it is more credible.